




LC REGULATION: 

OR REPRODUCING AN 
DOCUMENT, ALL C -Afe ,pi, LED' 
markings must be_ca icelle il 


declassified 

By authority Secretary §£ 

1 1960 

Defense memo 2 August I Mu 
LIBRARY OF CONGRgii 


V 




*3 


% yO* % 
§& 


^ ^S^a s 

V'!\ ^gsawW* 1 
HP ** 1 [t a««iw® 


?±C .REGULATION : BEFORE SERVICING 
OR REPRODUCING ANY PART OF THIS 
DOCUMENT, ALL CLASSIFICATION 
markings must’ b e cancelled: 




% 

w3« 


*2^ 


DECLASSIFIED 
By authority Secretary of 

SEP 1 1960 

Defense memo 2 August 1960 




A Vo A 


LIBRARY OF CONGRESS 



SUMMARY TECHNICAL REPORT 
OF THE 

NATIONAL DEFENSE RESEARCH COMMITTEE 


This document contains information affecting the national defense of the 
United States within the meaning of the Espionage Act, 50 U. S. C., 31 and 
32, as amended. Its transmission or the revelation of its contents in any 
manner to an unauthorized person is prohibited by law. 

This volume is classifief^^SM^BBHBBfc’ in accordance with security 
regulations of the War and Navy Dep artment s because certain chapters 
contain material which was*^B^|^HHHHfe at the date of printing. 
Other chapters may have had a lower classification or none. The reader is 
advised to consult the War and Navy agencies listed on the reverse of this 
page for the current classification of any material. 


Manuscript and illustrations for this volume were prepared for 
publication by the Summary Reports Group of the Columbia 
University Division of War Research under contract OEMsr-1131 
with the Office of Scientific Research and Development. This vol- 
ume was printed and bound by the Columbia University Press. 

Distribution of the Summary Technical Report of NDRC has 
been made by the War and Navy Departments. Inquiries concern- 
ing the availability and distribution of the Summary Technical 
Report volumes and microfilmed and other reference material 
should be addressed to the War Department Library, Room 
1A-522, The Pentagon, Washington 25, D. C., or to the Office 
of Naval Research, Navy Department, Attention: Reports and 
Documents Section, Washington 25, D. C. 


Copy No. 

238 


This volume, like the seventy others of the Summary Technical 
Report of NDRC, has been written, edited, and printed under 
great pressure. Inevitably there are errors which have slipped 
past Division readers and proofreaders. There may be errors of 
fact not known at time of printing. The author has not been able 
to follow through his writing to the final page proof. 


Please report errors to: 

JOINT RESEARCH AND DEVELOPMENT BOARD 
PROGRAMS DIVISION (STR ERRATA) 

WASHINGTON 25, D. C. 

A master errata sheet will be compiled from these reports and 
sent to recipients of the volume. Your help will make this book 
more useful to other readers and will be of great value in prepar- 
ing any revisions. 



SUMMARY TECHNICAL REPORT OF DIVISION 4, NDRC 


VOLUME 3 


SUMMARY, PHOTOELECTRIC 
FUZES AND MISCELLANEOUS 

PROJECTS 


OFFICE OF SCIENTIFIC RESEARCH AND DEVELOPMENT 
VANNEVAR BUSH, DIRECTOR 

NATIONAL DEFENSE RESEARCH COMMITTEE 
JAMES B. CONANT, CHAIRMAN 

DIVISION 4 

ALEXANDER ELLETT, CHIEF 


WASHINGTON, D. C., 1946 


NATIONAL DEFENSE RESEARCH COMMITTEE 


James B. Conant, Chairman 
Richard C. Tolman, Vice Chairman 
Roger Adams Army Representative 1 

Frank B. Jewett Navy Representative 2 

Karl T. Compton Commissioner of Patents 3 

Irvin Stewart, Executive Secretary 


1 Army representatives in order of service: 


Maj. Gen. G. V. Strong 
Maj. Gen. R. C. Moore 
Maj. Gen. C. C. Williams 
Brig. Gen. W. A. Wood, Jr. 

Col. E. A. 


Col. L. A. Denson 
Col. P. R. Faymonville 
Brig. Gen. E. A. Regnier 
Col. M. M. Irvine 
Routheau 


2 Navy representatives in order of service: 

Rear Adm. H. G. Bowen Rear Adm. J. A. Furer 

Capt. Lybrand P. Smith Rear Adm. A. H. Van Keuren 

Commodore H. A. Schade 
3 Commissioners of Patents in order of service: 
Conway P. Coe Casper W. Ooms 


NOTES ON THE ORGANIZATION OF NDRC 


The duties of the National Defense Research Committee 
were (1) to recommend to the Director of OSRD suitable 
projects and research programs on the instrumentalities of 
warfare, together with contract facilities for carrying out 
these projects and programs, and (2) to administer the tech- 
nical and scientific work of the contracts. More specifically, 
NDRC functioned by initiating research projects on re- 
quests from the Army or the Navy, or on requests from an 
allied government transmitted through the Liaison Office 
of OSRD, or on its own considered initiative as a result of 
the experience of its members. Proposals prepared by the 
Division, Panel, or Committee for research contracts for 
performance of the work involved in such projects were 
first reviewed by NDRC, and if approved, recommended to 
the Director of OSRD. Upon approval of a proposal by the 
Director, a contract permitting maximum flexibility of 
scientific effort was arranged. The business aspects of the 
contract, including such matters as materials, clearances, 
vouchers, patents, priorities, legal matters, and administra- 
tion of patent matters were handled by the Executive Sec- 
retary of OSRD. 

Originally NDRC administered its work through five 
divisions, each headed by one of the NDRC members. 
These were: 

Division A — Armor and Ordnance 

Division B — Bombs, Fuels, Gases, & Chemical Problems 
Division C — Communication and Transportation 
Division D — Detection, Controls, and Instruments 
Division E — Patents and Inventions 


In a reorganization in the fall of 1942, twenty-three ad- 
ministrative divisions, panels, or committees were created, 
each with a chief selected on the basis of his outstanding 
work in the particular field. The NDRC members then be- 
came a reviewing and advisory group to the Director of 
OSRD. The final organization was as follows: 

Division 1 — Ballistic Research 

Division 2 — Effects of Impact and Explosion 

Division 3 — Rocket Ordnance 

Division 4 — Ordnance Accessories 

Division 5 — New Missiles 

Division 6 — Sub-Surface Warfare 

Division 7 — Fire Control 

Division 8 — Explosives 

Division 9 — Chemistry 

Division 10 — Absorbents and Aerosols 

Division 11 — Chemical Engineering 

Division 12 — Transportation 

Division 13 — Electrical Communication 

Division 14 — Radar 

Division 15 — Radio Coordination 

Division 16 — Optics and Camouflage 

Division 17 — Physics 

Division 18 — War Metallurgy 

Division 19 — Miscellaneous 

Applied Mathematics Panel 

Applied Psychology Panel 

Committee on Propagation 

Tropical Deterioration Administrative Committee 


Library of Congress 


CONFIDENTIAL 


i 


IV 


2015 


490931 


FOREWORD 


A s events of the years preceding 1940 revealed 
. more and more clearly the seriousness of the 
world situation, many scientists in this country 
came to realize the need of organizing scientific re- 
search for service in a national emergency. Recom- 
mendations which they made to the White House 
were given careful and sympathetic attention, and 
as a result the National Defense Research Commit- 
tee [NDRC] was formed by Executive Order of the 
President in the summer of 1940. The members of 
NDRC, appointed by the President, were instructed 
to supplement the work of the Army and the Navy 
in the development of the instrumentalities of war. 
A year later, upon the establishment of the Office of 
Scientific Research and Development [OSRD], 
NDRC became one of its units. 

The Summary Technical Report of NDRC is a 
conscientious effort on the part of NDRC to sum- 
marize and evaluate its work and to present it in a 
useful and permanent form. It comprises some sev- 
enty volumes broken into groups corresponding to 
the NDRC Divisions, Panels, and Committees. 

The Summary Technical Report of each Division, 
Panel, or Committee is an integral survey of the 
work of that group. The report of each group 
contains a summary of the report, stating the prob- 
lems presented and the philosophy of attacking 
them, and summarizing the results of the research, 
development, and training activities undertaken. 
Some volumes may be “state of the art” treatises 
covering subjects to which various research groups 
have contributed information. Others may contain 
descriptions of devices developed in the labora- 
tories. A master index of all these divisional, panel, 
and committee reports which together constitute 
the Summary Technical Report of NDRC is con- 
tained in a separate volume, which also includes 
the index of a microfilm record of pertinent tech- 
nical laboratory reports and reference material. 

Some of the NDRC-sponsored researches which 
had been declassified by the end of 1945 were of 
sufficient popular interest that it was found desir- 
able to report them in the form of monographs, such 
as the series on radar by Division 14 and the mono- 
graph on sampling inspection by the Applied Mathe- 
matics Panel. Since the material treated in them is 
not duplicated in the Summary Technical Report 
of NDRC, the monographs are an important part of 
the story of these aspects of NDRC research. 

In contrast to the information on radar, which is 


of widespread interest and much of which is released 
to the public, the research on subsurface warfare is 
largely classified and is of general interest to a more 
restricted group. As a consequence, the report of 
Division 6 is found almost entirely in its Summary 
Technical Report, which runs to over twenty vol- 
umes. The extent of the work of a Division cannot 
therefore be judged solely by the number of volumes 
devoted to it in the Summary Technical Report of 
NDRC; account must be taken of the monographs 
and available reports published elsewhere. 

The program of Division 4 in the field of elec- 
tronic ordnance provides an excellent example of the 
manner in which research and development work by 
a civilian technical group can complement and sup- 
plement work done by the Armed Services. The 
greatest responsibility of Division 4, under the lead- 
ership of Alexander Ellett, was to undertake the 
development of proximity fuzes for nonrotating or 
fin-stabilized missiles, such as bombs, rockets, and 
mortar shells. 

Early work on fuzes of various types indicated 
that those operating through the use of electro- 
magnetic waves offered the most promise ; the even- 
tual device depended on the doppler effect, combin- 
ing the transmitted and received signals to create a 
low frequency beat which triggered an electronic 
switch. During the last phases of the war against 
Japan, approximately one-third of all the bomb 
fuzes used by carrier-based aircraft were proximity 
fuzes. For improving the accuracy of bombing oper- 
ations, the Division developed the toss bombing 
technique, by which the effect of gravity on the 
flight path of the missile is estimated and allowed 
for. The success of this technique is demonstrated 
by its combat use, when a circle of probable error 
as low as 150 feet was obtained. 

The Summary Technical Report of Division 4 
was prepared under the direction of the Division 
Chief and has been authorized by him for publica- 
tion. We wish to pay tribute to the enterprise and 
energy of the members of the Division, who worked 
so devotedly for its success. 

Vannevar Bush, Director 

Office of Scientific Research and Development 

J. B. Conant, Chairman 
National Defense Research Committee 


CONFIDENTIAL \ 


V 


FOREWORD 


T he primary program of Division 4, NDRC, was 
the development of proximity fuzes for bombs, 
rockets, and trench mortar projectiles. The Na- 
tional Bureau of Standards provided facilities and 
personnel for the Division Central Laboratories and 
the Division (or its predecessor, Section E of Divi- 
sion A) served as the principal liaison between 
NDRC and the National Bureau of Standards. The 
photoelectric fuze project formed a considerable part 
of the Division program during the first half of the 
war; a summary of work on that project comprises 
the major part of the present volume. Work on 
photoelectric fuzes was initiated in the fall of 1940 
by Section T at the Department of Terrestrial 
Magnetism under the able direction of L. R. 
Hafstad. In the summer of 1941, the project was 
transferred from Section T to Section E, and the 
work continued at the National Bureau of Stand- 
ards. Many of the project personnel were also trans- 
ferred, including, for a short period, Dr. Hafstad. 
After the project was well established in Section E, 
he returned to Section T, and Joseph E. Henderson 
carried on as project leader. The maintenance of 
effective liaison with the Army Ordnance Depart- 
ment is due largely to Colonel H. S. Morton, whose 
intelligent criticism and suggestions based on sound 
technical knowledge contributed much of value to 
the program. 

The development of photoelectric fuzes was under- 
taken because it was thought that a fuze of this 


type could be gotten into production more quickly 
than radio proximity fuzes. Actually this proved 
not to be the case, the radio fuze development 
(which is described in Volume 1 of Division 4) 
reaching the production point just as soon as the 
photoelectric fuze, so that the latter never went 
beyond the initial model. A further important con- 
sideration in the development of photoelectric fuzes 
was the plan of the Army Ordnance Department to 
provide an ammunition reserve of more than one 
basic type of proximity fuze for possible emergency 
use. The production of the T-4 photoelectric fuze 
was in fulfillment of this objective. 

The present volume also includes an overall sum- 
mary chapter of Division 4’s work, together with 
descriptions of work on projects later transferred 
from Division 4 and of work on several minor 
projects. Of the latter, the most important is the 
magnetic field extrapolating machine, which was 
effectively used by the Navy in connection with 
degaussing. The utility and feasibility of this device 
was first pointed out by G. Breit. The realization 
of the device in a practical form was due to J. W. M. 
DuMond, with the assistance of the Bell Telephone 
Laboratories in connection with the design of the 
production model. 

Alexander Ellett 
Chief, Division 4 


VI 


CONFIDENTIAL 


PREFACE 


T he projects dealt with in this volume (other 
than the Summary Chapter) are, generally, ter- 
minated or completed projects, in the sense that 
Division 4 was not engaged in active work on any 
of them (except the T-25 Project, Section 9.2) when 
World War II ended. In contrast, very active pro- 
grams were under way on radio proximity fuzes 
(Volume 1) and on the toss technique (Volume 2). 
Responsibility for further development on these 
two projects was assumed near the end of the war 
by the Army and the Navy. 

Work on photoelectric fuzes, which occupied a 
prominent part in the Division program for nearly 
three years, is summarized in Chapters 3 to 8, in- 
clusive, of this volume. Work on general fuze prob- 
lems is presented in Chapter 2, which serves as a 
summary of the proximity fuze program of the 
Division inasmuch as the relative merits of various 
types of proximity fuzes are compared therein. 
Other miscellaneous projects of the Division are 
summarized in Chapter 9. 

With the notable exception of the photoelectric 
fuze work, fairly complete termination reports were 
written on most of the projects covered in this 
volume. These terminating reports, which are in- 
cluded in the bibliographies, have been appreciably 
condensed for inclusion in this volume. In the case 
of the photoelectric fuze work, no overall termina- 
tion report was written, although work on the 


project ended in October 1943. The urgency of other 
projects in the Division (radio fuzes and toss bomb- 
ing) prevented the assignment of personnel to such 
report writing during the war. Hence Chapters 3 to 
8 of this volume represent the only overall summary 
of this once very comprehensive project. 

Credit is due Alex Orden for organizing the 
presentation of the photoelectric fuze work, as well 
as for writing three of the six chapters on the sub- 
ject. Other authors are named in the table of con- 
tents and in footnotes to the chapter or section 
headings. Where authorship is not specified, the 
material was prepared by the editor. 

Photographs in this volume were made by Theo- 
dore C. Hellmers, of the National Bureau of Stand- 
ards, unless credit is otherwise indicated. Drawings 
and graphs were prepared by the Drafting Group 
of the Ordnance Development Division of the 
National Bureau of Standards under the immediate 
supervision of E. W. Hunt. 

Considerable thanks are due R. L. Eichberg and 
Betty Hallman, of the National Bureau of Stand- 
ards, for valuable assistance in the review and 
assembly of final manuscript, and to Henrietta 
Leiner and Cecilie Smolen of the same organization, 
for the preparation of the bibliography. 

A. V. Astin 
Editor 


vii 


CONFIDENTIAL 






CONTENTS 


CHAPTER PAGE 

1 Summary of Work of Division 4 1 

2 Proximity and Time Fuzes 12 

3 Photoelectric Fuze Development; Introduction and 

Summary 20 

4 Basic Principles and Design of PE Fuzes by Alex Or den 

and R. F. Morrison 24 

5 Description of Photoelectric Fuze Types by Charles 
Ravitsky, T. M. Marion , W. E. Armstrong , and J. G. 

Reid, Jr 36 

6 Laboratory Methods for Testing T-4 Fuzes and Com- 
ponents by P. J. Franklin 59 

7 Field Test Methods for PE Fuzes by Alex Orden 70 

8 Evaluation of PE Fuzes by Alex Orden 75 

9 Miscellaneous Projects of Division 4 by Clarence B. 

Crane, L. M. Andrews, T. N. White, and Robert D. 
Huntoon 89 

Bibliography 101 

OSRD Appointees 109 

Contract Numbers 110 

Service Projects 113 

Index 115 


CONFIDENT! \l 


ix 



Chapter 1 

SUMMARY OF WORK OF DIVISION 


-mxo 


ii SCOPE 

T he work of Division 4, National Defense 
Research Committee [NDRC], was concerned 
primarily with problems in electronic ordnance. This 
involved the development of ways and means of 
increasing the effectiveness of weapons through the 
application of modern electronic techniques. Weapon 
effectiveness depends, in general, on three factors 
which are subject to control: (1) properties of the 
missile and its contents, (2) methods of aiming or 
directing the missile to its target, and (3) methods 
of controlling the detonation of the missile with re- 
spect to the target. Electronic ordnance is concerned 
primarily with the second and third factors, and 
remarkable advances in these fields were achieved 
during the period of World War II. The field of 
electronic ordnance, as defined, embraces not only 
the major work of Division 4, but also the work of 
many other NDRC divisions. 

Within the field of electronic ordnance, the work of 
Division 4 was concerned with proximity (variable 
time) [VT] fuzes for nonrotating or fin-stabilized 
missiles, such as bombs, rockets, and trench mortar 
shells, and with bomb directors. The work on these 
projects is summarized in Sections 1.2 and 1.3. The 
initiation of the bomb director project was closely 
related to problems pertaining to the use of VT 
fuzes. It was evident that, in order to bring bombs 
close enough to airborne targets for proximity ac- 
tion to be effective, the accuracy of bombing opera- 
tions had to be increased. This need led to the in- 
ception of the toss bombing technique, which is 
described in Section 1.3. A similar problem was en- 
countered by Section T, OSRD, in their work on 
proximity fuzes for rotating (spin-stabilized) pro- 
jectiles. In order for the VT shell fuzes to be effective 
in antiaircraft fire, methods of aiming had to be im- 
proved. This led to Section T’s participation in fire 
control development. 

As inferred in the preceding paragraph, responsi- 
bility for the development of proximity fuzes was 
shared by Division 4 and Section T, with the former 
handling fuzes for fin-stabilized missiles, and the 
latter, fuzes for spin-stabilized missiles. This divi- 


sion of responsibility, which was made for reasons 
of expediency and efficiency, proved very logical. 
The basic operating principles of the proximity 
fuzes developed were quite simple and were similar 
for both Division 4 and Section T fuzes. The major 
problem lay in adapting the design to the conditions 
of Service use and to a form which could be produced 
quickly in large quantities. In this, there proved to 
be basic differences in the fuzes for rotating and non- 
rotating missiles. These differences appeared in gen- 
eral mechanical layout and design, in the arming and 
safety features, and in the method of obtaining elec- 
trical power to operate the fuze. Taking the latter 
problem as an example, shell fuzes utilized the spin 
of the missile as an activating force for the power 
supply, whereas bomb fuzes were powered by elec- 
trical energy converted from mechanical energy, util- 
izing the airflow past the nose of the bomb. Still 
another difference between the power supplies for 
bomb and shell fuzes lay in the requirements for per- 
formance at very low temperatures. Bomb fuzes 
were required to perform reliably when cooled to the 
very low temperatures encountered by high-altitude 
bombers. An outstanding feature of most of the fuzes 
developed by Division 4 was a wind-driven electric 
generator which enabled the fuze to operate prop- 
erly when subjected to temperatures as low as 
-40 F. 

In addition to work on proximity fuzes and bomb 
directors, Division 4 pursued a number of other im- 
portant, but less extensive, projects. Some of these 
were related to fuze work; others were undertaken 
because of the availability of specialized personnel 
or facilities at Division 4’s Central Laboratories at 
the National Bureau of Standards. The miscellane- 
ous activities are listed in Section 1.4. 

The Summary Technical Report of Division 4 has 
been prepared in three volumes, as follows: Volume 
1, on radio proximity fuzes for bombs, rockets, and 
trench mortar shells; Volume 2, on bomb, rocket, 
and torpedo tossing; and Volume 3, containing, in 
addition to this overall summary chapter, descrip- 
tions of work on nonradio fuze^foartmuWlv nhoto- 
electric fuzes) and other ime e lumemis ordnance 
items. The introductor^gh^ii«nj{yV(aeffl5el^r»n6f 

■H SEP 1 1960 


Defense memo 2 August 1960 


LIBRARY OF .CONGRESS 



2 


SUMMARY OF WORK OF DIVISION 4 


2 contain rather complete summaries of the respec- 
tive projects. These chapters have been abstracted 
for presentation in Sections 1.2 and 1.3, which 
follow. 

12 RADIO PROXIMITY [VT] FUZES 
Selection of the Radio Method 

Proximity fuzes are intended to detonate missiles 
automatically upon approach to a target and at such 
a position along the flight path of the missile as to 
inflict maximum damage to the target. Various meth- 
ods of obtaining proximity operation against a tar- 
get were investigated : electrostatic, acoustic, optical, 
and radio. The relative merits of these methods are 
discussed in Chapter 2 of this volume. Prime con- 
siderations for a proximity fuze were reliability and 
simplicity. The former was necessary to insure per- 
formance under various stringent Service conditions, 
and the latter, to allow the fuze to be contained in a 
small volume and to be produced quickly in large 
quantities. Following initial exploratory investiga- 
tions, two types of fuzes, optical (photoelectric) and 
radio, were selected for intensive development. The 
photoelectric method was selected because it ap- 
peared as a relatively easy approach to the proxim- 
ity fuze problem, although the fuzes would be limited 
to daytime use, unless light sources were provided. 
The radio method appeared to be more complicated, 
but it afforded opportunity for reliable performance 
not only 24 hours a day but under a much wider 
variety of other conditions than were possible with 
the photoelectric fuze. The two methods were pur- 
sued in parallel until it was definitely established 
that radio proximity fuzes could be produced to ful- 
fill all requirements. When this stage of development 
was reached, work on photoelectric fuzes was ter- 
minated (October 1943), and the radio method was 
prosecuted even more vigorously than before. A brief 
summary of the achievements in the photoelectric 
program is given in Chapter 3 of this volume, and a 
more detailed presentation in Chapters 4 to 8, inclu- 
sive. 

How a Radio Proximity Fuze 
Operates 

Among various possible types of radio proximity 
fuzes, an active-type fuze operating on the doppler 


effect was selected as being the most promising 
method. 3 

In a doppler-type fuze, the actuating signal is pro- 
duced by the wave reflected from a target moving 
with respect to the fuze. The frequency of the re- 
flected wave differs from that of the transmitted 
wave, because of the relative velocity of fuze and 
target. The interference it creates with the trans- 
mitter results in a low-frequency beat caused by the 
combination of the transmitted and reflected fre- 
quencies. The low-frequency signal can be used to 
trigger an electronic switch. Selective amplification 
of the low-frequency signal is generally necessary. 

The principal elements of a radio proximity fuze 
are shown in block diagram form in Figure 1. 


ANTE NNA 



Figure 1 . Block diagram showing principal compo- 
nents of radio proximity fuze. 

Operation of the fuze occurs when the output sig- 
nal from the amplifier reaches the required ampli- 
tude to fire the thyratron. For a given orientation of 
the fuze and target, the amplitude of the target sig- 
nal produced in the oscillator-detector circuit is a 
function of the distance between the target and the 
fuze. Hence, by proper settings for the gain of the 
amplifier and the holding bias on the thyratron, the 
distance of operation may be controlled. Distance, 

3 See Cnapter 2 of this volume for a further discussion of 
active and passive fuzes, and Division 4, Volume 1, Chap- 
ter 1 for a discussion of other possible types of radio fuzes. 
Briefly, an active-type radio fuze includes both transmitting 
and receiving stations, whereas a passive-type fuze contains 
a receiving station only. Obviously, a passive-type radio 
fuze would require an auxiliary transmitter as part of the 
fire control equipment. 


CONFIDENTIAL 


RADIO PROXIMITY [YT] FUZES 


3 


however, is not the only factor which requires con- 
sideration. Orientation or aspect is very important, 
particularly against aircraft targets, since operation 
should occur at that point on the trajectory when 
the greatest number of fragments will be directed 
toward the target. 

For most missiles, the greatest number of frag- 
ments are directed upon detonation approximately 
at right angles to the axis of the missile. For trajec- 
tories which would normally pass by the target with- 
out intersecting it, there will be optimum chance of 
damage if detonation of the missile occurs when the 
target is in the direction of greatest fragmentation 
density. However, for trajectories which would inter- 
sect the target, the missile should come as close to 
the target as possible before detonation. Hence the 
basic requirements for directional sensitivity of a 
proximity fuze for antiaircraft use are: (1) the sen- 
sitivity should be a maximum in the direction 
corresponding to maximum lateral fragmentation 
density of the missile, and (2) the sensitivity should 
be a minimum along the axis of the missile. Direc- 
tional sensitivity of this type can be obtained by 
using the missile as an antenna, with the axis of the 
missile corresponding to the axis of the antenna. 
With the fuze in the forward end of the missile, such 
antennas are excited by means of a small electrode, 
or cap, on the nose of the fuze. Additional control 
over the sensitivity pattern of the fuze is possible by 
means of the amplifier gain characteristic. 

For use against surface targets, proximity fuzes 
are designed for an optimum height of burst, depend- 
ing on the nature of the target and the properties of 
the missile. These optimum heights of function vary 
from 10 to 70 ft for fragmentation and blast bombs 
and are of the order of a few hundred feet for chemi- 
cal warfare bombs. 

With a fuze intended for ground approach opera- 
tion, it is desirable to have maximum sensitivity 
along the axis of the bomb. A short dipole antenna 
mounted in the fuze transversely to the bomb’s axis 
gives such sensitivity. 

It was also found that fairly good ground approach 
performance could be obtained from fuzes with axial 
antennas by designing the amplifiers to compensate 
for the appreciable decrease in radiation sensitivity 
in the forward direction. For example, steep angles 
of approach generally mean high approach veloci- 
ties with higher doppler frequencies. Thus a loss in 


radiation sensitivity with steep approach can be 
compensated by an increase in amplifier gain for the 
higher doppler frequencies. 

A miniature triode is used for the oscillator in the 
fuze, and a pentode for the amplifier. Some fuzes use 
separate detector circuits with a tiny diode to pro- 
vide the required rectification. A miniature thyra- 
tron serves as the triggering agent, and a specially 
developed electric detonator initiates the explosive 
action. 

Energy for powering the electronic circuit is ob- 
tained, in the later fuze models, from a small electric 
generator. This is driven by a windmill in the air- 
stream of the missile. A rectifier network and volt- 
age .regulator are also essential parts of the power 
supply. 

The arming and safety features of the radio prox- 
imity fuzes are closely tied in with the power supply. 
This is a natural procedure since an electronic de- 
vice is inoperative until electric energy is supplied. 
Arming a radio proximity fuze (generator type) 
consists of the following operations: (1) either re- 
moval of an arming wire which frees the windmill, 
allowing it to turn in the airstream (bomb fuzes), 
or actuation of a setback device freeing the drive 
shaft of the generator, allowing it to turn (rocket 
and mortar shell fuzes), (2) operation of the genera- 
tor to supply energy to the fuze circuits, (3) connec- 
tion of the electric detonator into the circuit after 
a predetermined number of turns of the vane cor- 
responding to a certain air travel, and (4) removal 
of a mechanical barrier between the detonator and 
booster, prior to which explosion of the detonator 
would not explode the booster. Generally, operations 
(3) and (4) occur simultaneously by motion of 
the same device. These arming operations are indi- 
cated in the diagram in Figure 1. 

Additional safety is provided by the fact that un- 
less the generator of the fuze is turning rapidly the 
fuze is completely inoperative. A minimum airspeed 
of approximately 100 mph is required to start the 
generator turning. 

Sectioned models of two types of generator- 
powered radio fuzes for bombs are shown in Fig- 
ures 2 and 3. The fuze in Figure 2 uses the bomb as 
an antenna. It is a T-50 type fuze, frequently re- 
ferred to as a ring-type fuze. The fuze in Figure 3 
carries its own transversely mounted antenna. It is a 
T-51 fuze, frequently referred to as a bar-type fuze. 


CONFIDENTIAL 


L, 


4 


SUMMARY OF WORK OF DIVISION 4 



■FIRING UNIT 


POWDER TRAIN 


I 

TRANSMITTER 

RECEIVER 


GENERATOR 


ANTENNA 

GENERATOR PROPELLER 



Figure 2. Cutaway of ring-type, radio, bomb fuze 
(T-91E1). 


Figure 3. Cutaway of bar-type, radio, bomb fuze 
(T-51). 


Production of Radio Proximity 
Fuzes 

The course of the development of radio proximity 
fuzes for fin-stabilized missiles and the actual nature 
of the devices placed in production for Service use 
were influenced by many factors other than funda- 
mental technical considerations. Time and expedi- 
ency had a major influence on all designs. In order 
to have fuzes available for use as soon as possible, 
tooling for large production was frequently started 
before development was complete. This meant that, 
when changes in design became necessary or desir- 
able, the extent of such changes was largely con- 
trolled by the amount of retooling required or the 
delay which would be caused in production. Further- 
more, equipment design could not require compo- 
nents which would take too long to acquire in the 
necessary quantity, nor could overelaborate and 
time-consuming production techniques be consid- 
ered. 

Specific Service requirements varied as the course 
of World War II changed, and, because of the press- 
ing demand for speed, fuze designs for the new 
requirements made much more use of the tools and 
techniques employed in preceding models than if 


production had started out fresh. For example, early 
in World War II the greatest urgency was for anti- 
aircraft weapons, and stress was placed on fuzes for 
both bombs and rockets for this purpose. When the 
Allies acquired undisputed air superiority, the major 
proximity fuze requirements were shifted to the 
ground approach operation. Thus the T-50 type 
bomb fuze, which employs the axial radio antenna, 
ideal for antiaircraft use and initially designed for 
that purpose, was adapted to ground approach use. 
The T-51 fuze, which employs the transverse an- 
tenna specifically developed for ground approach 
use, was used much less extensively for this applica- 
tion because its initial lower priority made it avail- 
able later in the war. 

After the operation of a fuze design was found 
satisfactory by laboratory and field tests, it was 
necessary to determine its practicability for mass 
production. Pilot construction lines were used for 
this purpose, and it was the policy of Division 4 to 
require the construction of about 10,000 pilot line 
fuzes with suitable performance characteristics be- 
fore releasing a design to the Armed Services. 
Usually the tools developed for the pilot line work 
were used also for final production. Large-scale pro- 
curement was handled by the Services, but Divi- 


RADIO PROXIMITY [YT] FUZES 


5 


sion 4 participated in many phases of it, although 
largely in an advisory capacity. 

The radio proximity fuzes developed by Divi- 
sion 4 to the stage of large-scale production are as 
follows: 

M-8 Rocket Fuzes. T-5, an antiaircraft battery- 
powered fuze for the 4.5-in. M-8 rocket. This fuze 
is shown in Figure 4. Approximately 370,000 of 
these fuzes were procured by the Army. 



Figure 4. T-5 radio proximity fuze. Right view: 
fuze ready for loading in rocket. Middle view: assem- 
bled fuze (ready for screwing into housing and booster 
container, left). Middle view shows three principal 
components of fuze electronic assembly or nose (top), 
battery (middle), and safety and arming switch 
(bottom). 

T-6, a ground approach fuze, for use as an artil- 
lery weapon on the 4.5-in. M-8 rocket. This fuze is 
a variation of the T-5 fuze, having a longer arming 
time (about 6 sec compared to 1.0 sec) and no self- 
destruction element. It is identical in exterior ap- 
pearance with the T-5 fuze. Approximately 300,000 
of the T-5 fuzes were converted to T-6 fuzes after 
completion. 

Bomb Fuzes. T-50E1, a generator-powered 
ground approach fuze, for use primarily on the 
260-lb M-81 fragmentation bomb, the 100-lb M-30 
general purpose [GP] bomb, and the 2,000-lb M-66 
general purpose bomb. This fuze, which uses the 
bomb as a radio antenna, was planned for air-to-air 
use when development started, but was changed to 
ground approach application before development 


was completed. This fuze was set to arm after 3,600 
ft of air travel. In appearance it is very similar to 
the T-91 fuze shown in Figure 2. 

T-50E4 is similar to the T-50E1 except that its 
transmitter operates in a different frequency band, 
giving optimum performance on the 500-lb M-64 
and the 1,000-lb M-65 general purpose bombs. Ap- 
proximately 130,000 T-50E4 and T-90 fuzes were 
procured by the Army. 

T-89, an improved T-50E1 type fuze, giving more 
uniform burst heights. It also differs from T-50E1 
type fuzes in that arming setting can be checked 
more readily in the field. Approximately 140,000 
T-50E1 and T-89 fuzes were procured by the Serv- 
ices. This fuze is similar in appearance to the T-91 
fuze, shown in Figure 2. 

T-91 (later designation M-168), a variation of 
the T-89, developed specifically for low-altitude 
bombing to meet a naval requirement of higher 
burst heights than the T-89. This fuze is set to arm 
after 2,000 ft of air travel. Approximately 120,000 
T-91 fuzes were produced. This is the fuze shown in 
Figure 2. 

T-92, a variation of the T-90, developed to meet 
the same performance requirements as the T-91 of 
higher burst heights in low-altitude bombing. It is 
similar in appearance to the T-91 fuze. Approxi- 
mately 70,000 of these fuzes were produced. 

T-51 (later designation M-166), a generator- 
powered bomb fuze with a transverse antenna, for 
ground approach use on all general purpose, frag- 
mentation, and blast bombs of 100-lb size or larger. 
Burst heights with the T-51 are generally higher 
than with T-50 type fuzes. This fuze was set to arm 
after 3,600 ft of air travel. Approximately 350,000 
of these fuzes were procured by the Services. This 
fuze is shown in Figure 3. 

Later Rocket Fuzes. T-30 (Navy designation 
Mark 171), a generator-powered rocket fuze for air- 
to-air use, particularly on the Navy’s high-velocity 
aircraft rockets [HVAR] and 5-in. aircraft rockets 
[AR]. This fuze is physically very similar to the 
T-91 bomb fuze and only slightly different elec- 
trically. Its arming system is different in that the 
acceleration of the rocket is essential to its opera- 
tion. This fuze had just reached a production rate of 
10,000 per month at the end of World War II. 

T-2004 (Navy designation Mark 172), a gener- 
ator-powered rocket fuze for ground approach use. 
Similar to the T-30 but somewhat less sensitive and 



6 


SUMMARY OF WORK OF DIVISION 4 


has a longer arming time. Approximately 110,000 
of these fuzes were procured by the Services. 

Trench Mortar Fuzes. (Shown in Figure 5.) 
T-132, a generator-powered ground approach fuze, 
for use on the 81-mm trench mortar shell. This fuze 



Figure 5. Radio proximity fuzes for trench mortar 
shells. These are, from left to right, T-132. T-171. and 
T-172. The first two use the missile as an antenna, 
and the last carries its own antenna in the form of a 
loop. 

uses the body of the shell as an antenna. It also in- 
corporates a novel production technique, i.e., printed 
or stenciled electric circuits. Tools were being set up 
for a production rate of approximately 100,000 fuzes 
per month when World War II ended. 

T-171, a generator-powered, ground approach, 
mortar shell fuze, similar to the T-132, except that 
it employs the more standard circuit-assembly tech- 
niques. Tools were being set up for a production 
rate of about 125,000 per month when World War 
II ended. 

T-172, a generator-powered, ground approach, 
mortar shell fuze with a loop antenna. This antenna 
has essentially the same directional properties as the 
transverse antenna of the T-51 bomb fuze. Tools 
were being set up for a production rate of about 
250,000 fuzes per month. 

Figure 6 shows several typical missiles fuzed with 
radio proximity fuzes. 

Evaluation of Radio Proximity 
Fuzes 


be obtained from carefully planned effect-field trials. 
Evaluation tests which have been carried out on 
radio proximity fuzes can be grouped into the fol- 
lowing categories: (1) evaluation of conformance 
to requirements, and (2) evaluation as a weapon. 

1. Evaluation oj conformance to requirements. 
Based extensively on production acceptance testing, 
the reliability of the radio proximity fuzes foi 
bombs and rockets was about 85 per cent; that is, 85 
per cent of the fuzes would be expected to function 
on the target as required. Of the remainder, about 
10 per cent could be expected to function before 
reaching the target (random bursts) and 5 per cent 
not to function at all. The 10 per cent or so random 
functions were distributed along the trajectory be- 
tween the end of the arming period and the target. 
In many thousands of tests, no fuze functions were 
observed before the end of the arming period. 



Figure 6. Radio proximity fuzes assembled on mis- 
siles. Left, Mr. Harry Diamond, Chief of Ordnance 
Development Division, National Bureau of Standards 
(Division 4 central laboratories) and, right, Dr. Alex- 
ander Ellett, Chief, Division 4, NDRC. Fuzes and 
missiles are, left to right, T-132 fuze on 81-mm trench 
mortar shell (in Mr. Diamond’s hands) ; T-2004 fuze 
on HVAR rocket; T-2005 (experimental) fuze on 
HVAR; T-51 fuze on M-81 bomb; and T-91 fuze on 
M-64 bomb. A T-132 mortar shell fuze is in Dr. 
Ellett ’s hand. 

Reliability scores improved gradually throughout 
the production program, and the bomb and rocket 
fuzes which were in production at the end of World 
War II gave scores as follows: 


Although the final answer on the effectiveness of 
a new military weapon is supplied by its perform- 
ance in battle, the best quantitative measure of 
relative effectiveness under controlled conditions can 


T-91E1 fuzes 

92 per cent proper functions (average for 27 lots) 
7 per cent random functions 
1 per cent duds 


fCONFIDENTIAL 



RADIO PROXIMITY [YT] FUZES 


7 


The average height of function was 60 ft over a 
water target. 

T-51 fuzes (M-166) 

91 per cent proper functions (average on 230 lots) 

9 per cent random functions 
< 1 per cent duds 

The average height of function over the water tar- 
get was 110 ft. The proper function range included 
heights up to 200 ft for bar-type fuzes. 

T-2004 fuzes 

94 per cent proper functions (average on 75 lots) 
3 per cent random functions 
3 per cent duds 

The average height of the proper functions was 30 ft. 

2. Evaluation as a weapon. A careful analysis of 
the T-5 fuze on the M-8 rocket as an antiaircraft 
weapon was made by the Applied Mathematics 
Panel. The study was based on the experimental 
performance of the fuze against a mock aircraft 
target, fragmentation data of the rocket, dispersion 
data on the rocket when fired from an airplane, and 
vulnerability of a twin-engine enemy aircraft (in 
particular, the JU-88) to fragmentation damage. 

Conclusions of these studies were: (a) When fired 
from 1,000 yd directly astern with a standard devia- 
tion in firing error of about 50 ft (17 mils), a single 
round has 1 chance in 10 of preventing a twin-engine 
bomber from returning to base if it cannot return to 
base on 1 engine, (b) If return to base on 1 engine 
is possible, there is 1 chance in 16 that a single 
round will prevent its return, (c) If a delay of about 
50 ft were incorporated in the fuze (to bring the 
vulnerable part of the target in a region of greater 
fragmentation density), the above probabilities 
would be increased to 1 in 4 and 1 in 6. 

The probability of obtaining a crippling direct 
hit by an M-8 fired under the same conditions is 
about 1 in 100. 

Limited tests and evaluations were made of the 
5-in. AR and HVAR rockets equipped with T-30 
fuzes as antiaircraft weapons. At the Naval Ord- 
nance Test Station at Inyokern, California, some 
70 rounds were fired from a fighter airplane at a 
radio-controlled plane in flight. At about 400-yd 
range, more than 55 per cent of the rounds func- 
tioned on the target. Eight high-explosive [HE] 
loaded rounds were fired, 4 of which functioned on 


the target, and 3 of the 4 destroyed the targets. Pre- 
sumably, most of the rounds which did not function 
on the target were beyond the range of action of the 
fuzes. 

The Army Air Forces carried out extensive evalu- 
ations of the effectiveness of air burst bombs against 
shielded targets using T-50 and T-51 fuzes on the 
M-81 (260-lb fragmentation) and M-64 (500-lb 
GP) bombs. Bombs were dropped on a large effect- 
field covered with target boards 2x6 in. in trenches 1 
ft deep. The following conclusions are from the AAF 
report. 

For equivalent airplane loads of properly func- 
tioning bombs dropped on 12-in. deep trench tar- 
gets: 

1. Air burst 260-lb M-81 fragmentation bombs 
and 500-lb M-64 general purpose bombs produce 
about 10 times as many casualties as contact burst 
20-lb M-41 fragmentation bombs when trenches 
are 15 ft apart. (A casualty is defined as one or 
more hits per square foot, capable of perforating 
% in. of plywood.) 

2. Optimum height of burst for maximum casu- 
alty effectiveness is between 20 and 50 ft, with only 
slight variation through this range. 

The British carried out similar appraisals using 
T-50 fuzes on M-64 bombs. There are several dif- 
ferences in details of the tests, particularly in the 
matter of evaluating the effectiveness of surface 
burst bombs. The British Ordnance Board made an 
appreciable allowance for the blast effect of both 
the contact-fuzed bombs and VT-fuzed bombs and 
arrived at a superiority factor of 4 to 1 for the latter 
against shielded or entrenched targets. 

Studies by Division 2, NDRC, and by the British 
demonstrated that, when large blast bombs are air 
burst at about 50 to 100 ft above the ground, the 
area of demolition could be increased from 50 to 100 
per cent. No full-scale tests were carried out to 
verify these conclusions, but it was established that 
the T-51 fuze could be used on both the 4,000-lb 
(M-56) American bomb and the 4,000-lb British 
bomb to give air bursts at the proper altitudes. 

A number of evaluations were made to determine 
the effectiveness of air bursts for chemical bombs. 
In a carefully planned effect-field test using T-51 
and T-82 fuzes on 500-lb light-case bombs, the 
British showed that the areas of contamination with 
a mustard-type gas were 4 to 5 times greater than 
when the bombs were used with contact fuzes. The 


CONFIDENTIAL 


8 


SUMMARY OF WORK OF DIVISION 4 


increase was due to a more uniform distribution of 
the vesicant and avoidance of loss of material in 
craters. 

The Chemical Warfare Service and the British co- 
operated in an extensive series of tests at Panama, 
in simulated jungle warfare. A T-51 fuze with re- 
duced sensitivity effectively produced air bursts of 
chemical bombs below treetop canopies with efficient 
distribution of chemical materials. 

Weapon evaluations of the type described above 
depend on the properties of both the fuze and the 
missile. In no cases were the missiles designed for 
proximity operation. Now that proximity fuzes have 
been established as practicable devices, certain mis- 
siles, such as fragmentation bombs for air burst use, 
should be redesigned to increase greatly their effec- 
tiveness as weapons. 

Proximity fuzes for bombs and rockets saw very 
limited operational use, primarily because they were 
introduced into action very late in World War II. 
Altogether, approximately 20,000 fuzes, primarily 
bombs fuzes, were used in action by the Army and 
the Navy in the Pacific, ETO, and MTO. In the last 
few weeks of the Japanese War, approximately one- 
third of all the bomb fuzes used by carrier-based 
aircraft were proximity fuzes. The main targets 
were antiaircraft gun emplacements and airfields. 

No thoroughgoing analysis of the operational ef- 
fectiveness of the fuzes was possible, although the 
general reaction was very favorable. Since the fuzes 
were used in all theaters so late in World War II, 
the major uses were of a trial or introductory nature. 
In all cases, these trial uses were followed by urgent 
requests for more fuzes, which usually, and particu- 
larly in ETO and MTO, did not arrive until after 
World War II was over. Initial uses were all in 
1945: in February in the Pacific, and in March in 
ETO and MTO. Reports concerning the effective- 
ness of the fuzes against gun emplacement targets 
usually stated that the antiaircraft fire was either 
stopped or greatly reduced after the air burst bombs 
exploded. 

Although relatively little or no quantitative data 
as to the effectiveness of the fuzes were secured, 
their use was extensive enough to establish their 
practicability as Service items of ordnance equip- 
ment. Relatively little difficulty was experienced in 
the handling and use of the fuzes, and none of it was 
serious or unsurmountable. Hence, with the effec- 
tiveness of proximity fuzes well established by effect- 


field studies and their operational practicability 
established by combat use, proximity fuzes appear 
assured of a permanent and increasingly important 
position in modern ordnance. 

13 BOMB, ROCKET, AND TORPEDO 
TOSSING 

Toss bombing provides a method of improving 
the accuracy of bombing operations. The method 
can be used with bombs, rockets, and torpedoes, 
and, although applicable primarily to dive attacks, 
it is also effective in level, plane-to-plane attacks. 
In fact, the method can be employed wherever a 
collision course with the target can be flown for a 
short period prior to release of the missile. The ob- 
ject of the toss technique is to estimate and allow 
for the effect of gravity on the flight path of the 
missile. The latter is accomplished by releasing the 
missile from the aircraft with sufficient upward 
velocity above a line of sight to compensate for the 
gravity drop of the missile during its flight to the 
target. The release conditions are determined by an 
instrument which measures the time integral of the 
transverse acceleration of the aircraft during a pull- 
out above the line of sight and then releases the 
missile when this integral has reached the appro- 
priate value as required by the time of flight of the 
missile. The time of flight is computed by the instru- 
ment prior to pull-out, while the aircraft is flying a 
collision course toward the target. 

A typical toss-bombing attack is illustrated in 
Figure 7. The airplane enters a dive 2,000 to 5,000 ft 
above the point at which the projectile will be re- 
leased and attains speed as rapidly as feasible dur- 
ing this dive. When the speed has reached a value 
sufficiently high for operation, and with the sight 
properly oriented on the target, the normal bomb 
release switch is closed by the pilot. Two or three 
seconds after the beginning of the timing run, a light 
near the sight comes on, indicating that the pilot 
may commence pulling out of the dive. When the 
angle through which the airplane has pulled up 
reaches the proper size, as determined automatically 
by the instrument, the release of the missile occurs. 
At this instant, the signal light goes out, indicating 
to the pilot that release has occurred and that there- 
after he can employ any evasive action he desires. 

If, after the timing run has begun, the pilot de- 
cides not to complete the maneuver, the action of 


CONFIDENTIAL 


BOMB, ROCKET, AND TORPEDO TOSSING 


9 


the instrument can be stopped by merely opening the 
bomb release switch. This restores the electric cir- 
cuits to a standby condition. The equipment can be 



made operative again, even in the same dive if re- 
maining altitude and other conditions permit, by 
closing again the bomb release switch. 

The development of the toss-bombing instrument 
was originally undertaken to provide a means of 
attacking bomber formations by using fighter air- 
planes carrying bombs. It was initially planned to 
use a head-on approach with high closing speeds 
and relatively small gravity drops of the bombs 
after release. The development was carried far 
enough to demonstrate that the technique offered 
excellent advantages as a defensive weapon against 
formations of bombers. However, in view of the rap- 
idly increasing scale of the Allied air offensive at 
that time (late summer of 1943), the weapon was 
considered potentially more dangerous to Allied 
than to enemy operations. Work on the air-to-air 
portion of the project was therefore curtailed, and 
further development was directed toward applying 
the toss technique to dive bombing. 

With the use of the toss technique, much less skill 
is required of the pilot. No visibility below the nose 


of the plane is needed, the range at which a given 
accuracy can be attained is much greater, the time 
during which the airplane flies a predetermined 
course is very short (usually about 3 seconds) , and 
the pull-up preceding release constitutes an effective 
preliminary for evasive maneuvers should they be 
necessary. 

The tossing technique is particularly useful in the 
case of low-velocity, fin-stabilized projectiles, such 
as bombs and the 11.75-in. aircraft rockets, since it 
removes the restriction on range which, in the case 
of the depressed sight technique, is imposed by lim- 
ited visibility over the nose of the airplane. 

In a series of evaluation tests in which slant 
ranges varied from 5,400 to 9,300 ft, 747 bombs were 
tossed. The pilots allowed for wind, using aerological 
data and the wind error indicated by the first bomb. 
In general, 5 bombs were dropped in succession. 
Fifty per cent of all the bombs were within a circle 
of 100- ft radius drawn about the target. When the 
pattern of impacts was projected onto a plane nor- 
mal to the line of flight, 50 per cent of the impacts 
fell within a circle having a radius of 11.5 mils. As 
for the errors in range, 50 per cent of the impacts 
showed an error of less than 61 ft on the ground, 
or 5.8 mils normal to the line of dive. The corre- 
sponding deflection errors were 52 ft on the ground 
and 7.8 mils normal to the line of dive. 

The impact pattern of 82 5.0-in. high-velocity 
aircraft rockets, launched in pairs with rocket-toss- 
ing equipment, showed that 50 per cent of the rock- 
ets lay within a circle of 9.6 mils radius normal to 
the line of dive. Fifty per cent of the rounds deviated 
from the main point of impact by less than 6.3 mils 
in range and 7.4 mils in deflection. 

The toss equipment was used on a limited number 
of combat missions, in which it gave a circle of prob- 
able error [CPE] of 200 ft for all rounds released. 
Throwing out several rounds where misidentifica- 
tion of the target was established, the CPE drops to 
150 ft. 

All the data obtained by Division 4 in the rocket 
evaluation tests, and about half the data in the 
bomb evaluation tests, were obtained using experi- 
mental equipment designated as Bomb Director 
Mark 1, Model 0, AN/ASG-10XN. Modifications 
were made to the equipment to enable it to release 
rockets. The other half of the data in the bomb 
evaluation tests was obtained using production 
equipment for the release of bombs, designated as 


CONFIDENTIAL 


10 


SUMMARY OF WORK OF DIVISION 4 


Bomb Director Mark 1, Model 1, AN/ASG-10. Pro- 
duction equipment for the release of both bombs and 
rockets was designated as Bomb Director Mark 1, 
Model 2, AN/ASG-10 A. The first production model 
was Service tested just before the end of World War 
II with satisfactory results. A later model, desig- 
nated as Bomb Director Mark 2, AN/ASG-10B, 


production of the Model 0 units. Facilities were set 
up for production at an ultimate rate of 1,000 per 
month. This rate was not reached, because of the 
conclusion of World War II. Division 4 withdrew 
from the project during August of 1945, at which 
time the Navy Department took over sponsorship 
of further development and production. 



Figure 8. Components of Mark 1, Model 1, Bomb Director, less connecting cables. 


had reached the experimental stage at the end of the 
war. 

The Mark 1, Model 0 equipment was manufac- 
tured as rapidly as possible in order to serve as a 
pilot model to work out production difficulties, as 
well as to get equipment into the hands of the Serv- 
ices for immediate use. Of this model, 500 sets were 
delivered to the Navy, which, in turn, transmitted 
300 of them to the Army. Half of these 300 were 
sent to the European Theater, where some were used 
on 13 combat missions in P-47 airplanes. 

The Mark 1, Model 1 equipment, shown in Fig- 
ure 8, was developed on a contract basis during the 


14 MISCELLANEOUS PROJECTS 

The work of Division 4 included survey investi- 
gations of various types of proximity fuzes other 
than the radio and photoelectric methods. Work on 
acoustic, electrostatic, and pressure-actuated devices 
(see Chapter 2) was carried far enough to establish 
that radio methods were superior. Work was also 
done on electrically adjusted time fuzes, but only as 
an interim project to the development of reliable 
radio fuzes. 

Other projects of the Division included: 

1. Development of rockets for use in testing prox- 
imity fuzes. 



MISCELLANEOUS PROJECTS 


11 


2. Initiation of development of target rockets for 
AA gunnery training, later taken over by Divi- 
sion 3. 

3. Development of a new 81 -mm trench mortar 
shell (in cooperation with the Engineering and Tran- 
sitions Office) of improved ballistic properties, par- 
ticularly when VT-fuzed. 

4. Development of a machine for speeding up the 
computations involved in the degaussing of ships. 

5. Initiation of a controlled-trajectory bomb 


(guided missile) project, later taken over and com- 
pleted by Division 5. The controlled missiles were 
ultimately known as the Pelican and the Bat. b 

6. Development of methods of treating cotton as 
a substitute for silk in powder bags. 

The miscellaneous projects are summarized in 
Chapters 2 and 9. 


b Reports of Division 5 should be consulted for further 
information on these important projects. 


CONFIDENTIAL 



Chapter 2 

PROXIMITY AND TIME FUZES 


2.1 INTRODUCTION 

211 Classification of Fuzes 

A fuze is the mechanism which initiates the det- 
onation of a missile. Fuzes may be classified in 
several ways, the two most common criteria being 
(1) according to the manner of triggering the explo- 
sive train, and (2) according to the position of the 
fuze with respect to the intended target. These may 
be expressed more briefly as classification with re- 
spect to design or use. The two methods of classifi- 
cation are, of course, closely related since the 
requirements of use will be reflected in the principles 
of design. Classification with respect to use may be 
grouped under three major headings, namely: (1) 
operation along the trajectory before reaching or 
while passing the target, (2) operation at the end 
of the trajectory at impact with the target, and (3) 
operation after impact with the target, usually after 
penetration into the target. In the two latter appli- 
cations, either the deceleration of the missile at im- 
pact or the force of impact may be used to provide 
the energy necessary to initiate the fuze action. 
Such fuzes are variously referred to as contact, im- 
pact, inertia, or point-detonating. To secure func- 
tion after contact with or penetration into a target, 
either a delayed action device may be initiated by 
the impact force, or a clock, started at the launching 
of the missile, may be used. The latter method is 
applicable only for relatively long delay times, or 
for cases when the accurate timing of the delay is 
unimportant. To secure function of the fuze before 
impact, the impact force is, of course, not available, 
and other methods of operation must be employed. 
An examination of these possible other methods is 
the object of this chapter. 

There are two general methods by which opera- 
tion of a fuze on a missile in flight [category (1) 
in the preceding paragraph] may be obtained. One is 
by timing, and the other is by proximity action with 
respect to the target. Both methods were investi- 
gated by Division 4. Detonation of a missile in 
flight is often called an air burst, a term which will 
be used frequently in this chapter. 

Before discussing various types of time and prox- 
imity fuzes, it is desirable to review briefly the im- 


portant applications of air bursts, since the intended 
use has an important bearing on the principles of 
design. 

2,1,2 Advantages of Air Burst a 

Targets for air burst missiles are primarily either 
airborne or surface targets. In the case of airborne 
targets, the objective of air burst action is to in- 
crease the effective size of the target so that it is not 
necessary to score a direct hit in order to damage or 
destroy the target. If, for example, a missile can be 
detonated in passing a target so as to damage it at 
distances up to 50 ft from its center, then the effec- 
tive target area will be a circle of 50-ft radius. If the 
projected area of the target normal to the trajectory 
is 50 sq ft, then the target area will be increased 
over 150 times. Problems introduced by aiming er- 
rors and ammunition dispersion are thus greatly 
simplified. In the cases where such aiming and 
ammunition dispersion are large compared to the 
actual size of the target, the chances of producing 
damage are enormously increased. 

The antiaircraft fuze problem, however, requires 
more than merely producing detonation within a 
specified distance (determined by the lethal range 
of the missile’s fragments) of the target. The mis- 
sile must be properly oriented with respect to the 
target. This requirement arises because the distribu- 
tion of fragments from the exploded missile is not 
uniform in all directions. Usually the greatest num- 
ber of fragments are projected approximately at 
right angles to the axis of the missile. Accordingly, 
the target should be in the direction of greatest frag- 
mentation density at the instant of detonation if 
optimum effectiveness is to be obtained. 

In the case of surface targets, the object of air 
burst action is to enhance the effectiveness of the 
lethal agents, which may be fragments, chemicals, or 
blast. 

Air burst of a missile will allow the fragments to 
strike targets which would otherwise be protected 
or shielded from a contact burst, thus increasing the 
probability of damage. If, for example, the target 

a These advantages are discussed in more detail in Divi- 
sion 4, Volume 1, Chapters 1 and 9. 


12 


CONFIDENTIAL 


INTRODUCTION 


13 


is a man in a foxhole, it is a matter of simple geom- 
etry to show that because of the shielding effect of 
the walls of his trench, he will be protected from 
fragments from any surface burst except very close 
or direct hits. However, he will be exposed to frag- 
ments from any air burst visible from his foxhole 
and within lethal range. Thus an air burst increases 
the probability of damage, and, as in the antiaircraft 
case, increases the effective size of the target in the 
sense that missile trajectories do not have to inter- 
sect the target to damage it. A number of evalua- 
tions have been carried out concerning the optimum 
height for air burst against shielded targets. 13-19 
These heights vary with a number of factors but 
generally fall within the range of 10 to 50 ft. 

If it is desired to produce damage by blast, it has 
been found that air burst enhances the effect. Areas 
of demolition and minor damage as well are in- 
creased approximately 50 to 100 per cent by an air 
burst in the proper height range. 8 For the 4,000-lb 
M-56 bomb, the optimum height is usually be- 
tween 40 and 70 ft. 

If it is desired to cover an area with a chemical 
such as mustard gas or smoke, air burst of the mis- 
sile containing the chemical increases the area of 
contamination. In this application, the chemical is 
distributed more uniformly over a wider area and 
without the loss of material in a crater. Optimum 
heights of function for this application have not 
been finally determined but appear to be of the 
order of 200 to 500 ft. 12 

2,1,3 Types of Air Burst Fuzes 

The production of air bursts with time fuzes re- 
quires accurate knowledge of range. Against station- 
ary ground targets at fairly short range, it is pos- 
sible in artillery fire to obtain excellently placed 
air bursts with time fuzes. With longer ranges or 
against moving targets (involving a continuously 
varying range), the reliability of the air burst be- 
comes less certain. Also, in bombing operations, 
satisfactory air burst cannot be obtained with time 
fuzes except from very low altitudes of release. 
Against aircraft targets, the problem with time fuzes 
is still more critical. Not only does the range vary 
continually, but the requirement for optimum effect 
(that detonation occur at the point on the trajectory 
where the greatest number of fragments will en- 
velop the target) places severe demands on range 


determination and fuze accuracy. Modern radar- 
ranging techniques increased greatly the accuracy 
of range determinations and gave impetus to the 
development of more accurate time fuzes which 
could be quickly and automatically set at the time 
of firing. Work done by Division 4 on the develop- 
ment of such fuzes for antiaircraft rockets is dis- 
cussed in Section 2.2. 

Properly designed and reliable proximity fuzes 
greatly simplify fire control problems, and greatly 
increase the probability of damage. If the design of 
a proximity fuze is right, the fuze will detonate the 
missile automatically at the proper point of its tra- 
jectory to inflict maximum damage. No setting of 
the fuze on the basis of range estimates, before 
launching the missile, will be necessary. It is under- 
standable, however, that the various applications 
mentioned above may require proximity fuzes of 
somewhat varying design. 

In order that a fuze operate automatically on 
proximity to a target, it is necessary that it be sen- 
sitive to some form of energy which is either emitted 
by the target or emitted by some other source and 
reflected or absorbed by the target. Various forms 
of energy-sensitive devices which have been investi- 
gated or seriously considered by Division 4 are air 
pressure, acoustic, electrostatic, and electromagnetic, 
the latter including both the optical and radio- 
frequency portions of the spectrum. Magnetic de- 
vices were not investigated primarily because 
magnetic sensitivity varies as the inverse cube of 
distance and an apparatus with suitable magnetic 
sensitivity would probably have been too bulky for 
other than underwater missiles. Fuzes for the latter 
were not within the cognizance of Division 4. The 
relative merits of the above-mentioned types of 
energy-sensitive devices are discussed in Sections 
2.3 to 2.7, inclusive. 

Proximity fuzes, regardless of the form of energy 
to which they are sensitive, may be divided into 
two general classes: active and passive. An active- 
type fuze carries a source of energy which is radi- 
ated and then picked up after reflection from a 
target. A passive-type fuze is merely sensitive to 
energy incident on the fuze. In order for a passive- 
type fuze to indicate proximity to a target, either the 
target must be a source of energy or an auxiliary 
source must be available or provided to radiate the 
necessary controlling energy. Thus a passive-type 
fuze would be of simpler design and construction 


CONFIDENTIAL 


14 


PROXIMITY AND TIME FUZES 


than an active fuze. However, if an auxiliary source 
of energy has to be provided for the passive fuze, 
the overall system might well be more complicated 
operationally than for an active fuze. 

The particular form of energy-sensitive device 
selected for fuze operation must be adaptable to 
the ballistic properties of the missile which is to be 
detonated. It was found that the principles of fuze 
operation and auxiliary equipment (power supply, 
safety features, etc.) depended closely on the prop- 
erties of the missile. For this reason, fuze develop- 
ment was carried out under two general headings: 
(1) fuzes for spin-stabilized missiles, and (2) fuzes 
for fin-stabilized missiles, including bombs, rockets, 
and trench mortar shells. Division 4 was charged 
with responsibility for fuzes in the second category, 
and the following discussion is limited to that ex- 
tent. b 

2 2 RC TIME FUZES 

2,21 Introduction 

The production of air bursts with time fuzes, even 
with means available to obtain extremely accurate 
range data, may be considered as an interim method, 
prior to the development of an ideal proximity fuze. 
It w r as from this point of view that work, described 
in the next two sections, was done on time fuzes for 
two rockets, the British 3.25-in. antiaircraft rocket 
and the U. S. Army 4.5-in. M-8 rocket. The projects 
were terminated before completion for two reasons: 
(1) satisfactory radio proximity fuzes were devel- 
oped, and (2) the rockets for which the fuzes were 
developed became obsolete for antiaircraft use. 

A major advantage of a reliable time fuze over a 
nonideal proximity fuze is its independence of exter- 
nal stimuli after launching. Since a proximity fuze 
is by its very nature subject to external influence, it 
should be possible to introduce, in defense, factors 
which would cause the proximity fuze to malfunc- 
tion or to operate on a false target. The production 
of such factors is called countermeasures, a subject 
which is beyond the scope of this volume. 0 However, 
the design of a fuze which would be highly resistant 
to countermeasures was a fundamental considera- 
tion in all fuzes developed by Division 4. Thus the 

b For information concerning work done on fuzes for spin- 
stabilized missiles, reference is made to the reports of Section 
T, OSRD. 

c See reports of Division 15, NDRC. 


immunity of a time fuze to countermeasures was 
important. 

Another closely allied advantage of the time fuze 
was its relative lack of dependence on the properties 
of the missile after launching. This was particularly 
important in the case of rockets because of a phe- 
nomenon known as afterburning. In most rockets, 
the propellant does not burn completely during the 
main accelerating period but continues to burn 
sporadically for several seconds afterward. This 
afterburning may interfere with the proper opera- 
tion of a radio proximity fuze. d Although the prob- 
lem was ultimately resolved for the radio proximity 
fuzes (largely through redesign of the rockets), its 
initial serious nature gave priority to time fuze 
development for rockets for some time. 

Electronic methods were selected over mechanical 
methods for the timing operations because of the 
easy and rapid adjustment of the time setting that 
the former afforded. The electronic circuits con- 
sisted essentially of a resistance-capacitance [RC] 
charging network and a thyratron. The latter fired 
an electric detonator to initiate the explosive action. 

22 2 Fuze for 3.25-in. British 

UP Rocket 

The development of an electric time fuze for 
use especially in high-altitude antiaircraft rockets 
(British 3.25-in. UP) was undertaken by the Re- 
search Laboratory of the General Electric Company 
under Contract OEMsr-99. A full summary of the 
development to termination is given in reference 7. 
The problem was to produce an accurate time fuze 
which could be set, by a simple voltage adjustment 
at the time of launching, to operate at times from 1 
to 20 seconds. A simple setback arming switch was 
required which would keep the fuze safe for normal 
handling and operate to perform the necessary 
switching operations when subjected to a sustained 
acceleration of from 25 to 40 g. 

The circuit elements, less switches, of the system 
developed are shown in Figure 1. The circuit con- 
tains a small impulse thyratron that discharges the 
anode capacitor through an electric detonator (not 
shown) when the grid potential ceases to be nega- 
tive. Anode and grid capacitors are made equal. At 
time t = 0, an external voltage, which has main- 
tained the anode at potential V aQ and the grid at 

d See Division 4, Volume 1. 


CONFIDENTIAL 


RC TIME FUZES 


15 


potential — V 0o is disconnected from the circuit. 
The grid and anode potentials then drift toward 
their common asymptote. If the thyratron fires when 
V g reaches zero potential, it can be shown that the 



Figure 1. Circuit elements, less switches, for RC 
time fuze for 3.25-in. rocket. 


setback to open and close the contacts indicated. 
This element also carried a 1. 5-volt dry cell to heat 
the filament of the thyratron. The anode and grid 
bands were contacts on the exterior surface of the 
fuze to allow charging of the capacitor just prior to 
launching of the rocket. The capacitors were 1.1 
microfarad and of the oil-impregnated paper type. 
The load resistors were 16-, 17-, and 18-megohm 
resistors (total 51 megohms) with low temperature 
coefficients. The thyratron was a special miniature 
type possessing excellent rugged characteristics. 

Field tests on approximately 100 fuzes were con- 
ducted at the Aberdeen Proving Ground. Se venty - 
five per cent of the fuzes functioned with time varia- 
tions as follows: 


Expected Time 
(seconds) 


Extreme Observed Deviation 
(seconds) 


6.20 - 0.13 to - 0.05 

15.28 - 1.11 to + 0.07 

20.26 -11.2 to +13.5 


firing time depends solely upon the ratio 
Thus the time of operation can be controlled by a 
simple potentiometer which varies the zero potential 
point of a total voltage applied across the points 


TRIMMING 

RESISTOR 



Figure 2. Complete circuit diagram for RC time; fuze 
for 3.25-in. rocket. 


a and g. This circuit was based on a British develop- 
ment known as the Benjamin circuit. 

A circuit diagram of a completed fuze is shown 
in Figure 2. The element marked S moved down on 


The deviations on the short time were considered 
quite good. No satisfactory explanations were found 
for the unusual deviations at the 20-second setting. 
The load resistors were the least satisfactory part 
of the circuit, and it was realized that considerably 
improved reliability could be expected if better re- 
sistors were developed. There was also some indica- 
tion that the method of removing the external 
capacitor-charging contact at firing interfered with 
the proper operation of the timing circuit. 

223 Fuze for U. S. Army 4.5-in. 

M-8 Rocket 

Development of a fuze for the 4.5-in. M-8 rocket 
was undertaken by the University of Florida under 
Contract OEMsr-949. 9 A starting point was the cir- 
cuit described in Section 2.2.2 modified to allow the 
use of smaller resistors. In addition, greater stability 
was introduced in the circuit by connecting the grid 
to ground through a high-value resistor. A simplified 
circuit (less switches) is shown in Figure 3. The 
capacitors C i and C 2 are initially charged with the 
polarities shown with V 10 larger than V 20 . The volt- 
ages are maintained at their initial values by an 
external source until the instant of firing, at which 
time the external source is removed and the two- 
mesh RC network begins to discharge. When the 
grid-to-cathode voltage, originally negative, becomes 
approximately zero, the thyratron fires. The firing 


C( NFIDENTIAL 


i 


16 


PROXIMITY AND TIME FUZES 



Figure 3. Circuit elements, less switches, for RC 
time fuze for 4.5-in. M-8 rocket. 


time for optimum circuit conditions {R 1 = R 2 
and Ci = C 2 ) is shown, as a function of the ratio 
F 20 /F 10 in Figure 4. Accurate times were obtained 
by careful matching of the resistors and capacitors. 


not so satisfactory because of difficulties with the 
external charging device. These difficulties did not 
appear insurmountable, but they had not been 
resolved when the project was terminated. 



* \ 



Figure 4. Firing times for RC time fuze as function 
of initial voltages. 


In structure, the fuze followed the mechanical out- 
line of the T-4 photoelectric [PE] fuze (see Fig- 
ure 2, Chapter 3) and also the T-5 radio fuze. 6 These 
two proximity fuzes were also intended for use on 
the M-8 rocket. The setback switch for the time 
fuze was the same as used in the proximity fuzes. 

A photograph of the fuze is shown in Figure 5. 
The charging rings may be seen at the tip of the 
ogive. Excellent results were obtained in laboratory 
tests; 50 per cent of the firing times at 20 seconds 
were within 0.2 second. In field tests, results were 
e See Division 4, Volume 1. 



Figure 5. Views of RC time fuze for M-8 rocket. 
Top shows electronic components. Lower view shows, 
from left to right, assembled fuze with charging rings 
on ogive, switch, and fuze container. (University of 
Florida photograph.) 

2 2,4 Capacitor Investigations 

In connection with the development of RC time 
fuzes, and also for possible use in the filter circuits 
of generator-powered radio fuzes, 6 investigations 
were carried out on various dielectric materials to 
obtain a capacitor with improved space factor. 10 ’ 11 
Both flexible and rigid designs were studied. A satis- 
factory design was obtained using a titanium mix- 
ture (No. 1242) as powder with a varnish binder as 
a flexible coating on tin foil. Two pieces of coated 
tin foil could then be rolled to make a tubular ca- 


CONFIDENTIAL 



ACOUSTIC FUZES 


17 


pacitor. Dielectric constants of 50 to 70 were ob- 
tained with power factors as low as 3 per cent. 

2 3 PRESSURE FUZES 

Air bursts can be produced on bombs by means 
of barometric or pressure-actuated devices. Such 
fuzes require for reliable operation precise knowl- 
edge of the ground pressure and release altitudes. 
Even so, the atmospheric pressure gradient is too 
small to obtain satisfactory operation in the 20- to 
50-ft height range required for optimum fragmen- 
tation effect. Subject to the limitations mentioned, 
satisfactory operation of a barometric fuze might be 
expected at altitudes of 1,000 ft or higher. 

No actual development was done by Division 4 on 
a strictly barometric fuze, but a combination baro- 
metric and time device (called a barotimer) was 
studied for use on bombs. 5 In this device, a clock- 
work time fuze is set continuously while in the air- 
plane by a flexible sylphon, the extension of which 
varies with the atmospheric pressure at the altitude 
of flight. The sylphon sets the time fuze to the time 
that will be needed for the bomb and fuze to fall a 
desired distance. At the moment of release, an arm- 
ing wire disconnects the fuze-setting sylphon from 
the clock and frees the clockwork. Thus, after the 
barotimer leaves the plane, the barometric time- 
setter has nothing further to do with the operation 
of the barotimer. 

Although reliable laboratory operation to within 
0.05 second was obtained, corresponding to drops 
from 4,000 to 12,000 ft, no field tests were conducted. 
It was concluded that, because of inherent variations 
in atmospheric pressure and possible lack of knowl- 
edge of the altitude (and pressure) at the target, the 
burst heights would be too variable. Accordingly, 
the project was terminated, and effort was diverted 
to other methods for obtaining air bursts. 

Another type of pressure-actuated device for pro- 
ducing air burst was developed by the British. This 
fuze, called the No. 44 Pistol, contains a pressure- 
sensitive diaphragm which triggers the explosive 
action when subjected to a sudden increase in pres- 
sure. Air bursts of bombs are obtained by dropping 
several bombs fuzed with the No. 44 Pistol in a 
stick or train. The first bomb in the train explodes 
on impact or an inch or two before impact. The 
blast effect from the first bomb causes the other 


bombs to burst in the air. Usually about 50 per cent 
air burst operation is obtained in sticks of four 
bombs. 

Evaluation of the method showed it to be about 
half as effective as radio proximity fuzes. 20 

2 4 ELECTROSTATIC FUZES 

Considerable survey was done (under Section T, 
OSRD) concerning the possible use of electrostatic 
methods to produce air bursts, particularly for the 
antiaircraft application. The electrostatic method 
was very appealing, primarily because of its sim- 
plicity. 

Operation of an electrostatic fuze depends on the 
electric charge on the target or on the missile or on 
both. The conclusions of the Section T investigations 
were that the charges on aircraft in flight and on the 
missile were too variable to insure reliable proximity 
operation. 2 

It is interesting to note that, in German attempts 
to develop a proximity fuze, their most advanced 
design was based on the electrostatic principle. Al- 
though results of German investigations concerning 
the charge on an airplane in flight were in reasonable 
agreement with American results, the Germans de- 
cided to accept the low sensitivity which such fuzes 
should have. 

2 5 ACOUSTIC FUZES 

The noise generated by aircraft in flight suggests 
the possibility of an acoustic type of passive prox- 
imity fuze for antiaircraft operation. It appeared 
that an extremely simple and reliable antiaircraft 
fuze could be designed and produced, provided that 
the noise generated by the missile itself did not in- 
troduce complications. Accordingly, extensive tests 
were conducted both by Division 4 (then Section E) 4 
and Section T 3 to evaluate the noise generated by 
missiles in flight. Levels of sound intensity were 
measured both in wind tunnels and on missiles in 
flight. 6 The general conclusion was that the self-noise 
in the missile exceeded the noise level produced by 
the airplane at distances at which proximity opera- 
tion was desired. 

Various locations for a fuze in a bomb were inves- 
tigated and it appeared that a nose location offered 
the best signal-to-noise ratio. Frequency-selective 


CONFIDENTIAL 


18 


PROXIMITY AND TIME FUZES 


devices were also studied, and it appeared that great- 
est discrimination between self-noise and target 
noise would be obtained in the region between 200 
and 1,000 c. 4 

A number of schemes were proposed and some 
were studied for obtaining an adequate signal-to- 
noise ratio. One of the most promising involved the 
use of two microphones which would receive the tar- 
get signal in equal phase and self-noise in random 
phase. Other systems involved working on rapid 
variations in noise gradient in selected frequency 
bands. Although it did not appear that an acoustic 
proximity fuze was impossible, it did seem that 
more effort would be required to obtain a satisfac- 
tory fuze of the acoustic type than for other types 
under consideration. Also, the velocity of sound ap- 
peared as a major limitation in the design and use 
of an acoustic fuze, particularly in high-speed 
missiles against high-speed aircraft. 

The Germans had a large number of acoustic fuze 
projects, but none passed the development stage. In 
one of these (Kranich, an entirely mechanical de- 
vice) , the self-noise problem appeared to have been 
eliminated by a simple balancing scheme. This fuze 
operated on the doppler shift in noise frequency on 
passing the target. 

26 OPTICAL FUZES 

Designs for optical proximity fuzes can be consid- 
ered for both passive or active operation. The sim- 
plest is, of course, the passive type, in which the fuze 
consists essentially of a light-detector. In the anti- 
aircraft case, the target is a source of infrared radia- 
tion, which can be used to indicate proximity to a 
target. This principle, however, was not considered 
seriously until late in World War II, because earlier 
the available infrared detectors were too slow or too 
insensitive in response to be considered in fuzes. 
Another type of passive optical fuze uses the sun as 
a source of energy, the target as an interceptor or 
modulator of the energy, and a photoelectric cell 
as the sensitive detecting element within the fuze. 
Such a system offers a simple and straightforward 
basis for an antiaircraft fuze design, and the prin- 
ciple was exploited extensively by Division 4. The 
results of the investigations are presented in Chap- 
ters 3 to 8 of this volume. 

A passive type of photoelectric fuze was developed 


by the British very early in World War II, and their 
work provided a starting point for American devel- 
opment. The results of the initial American survey 
on the possibilities of photoelectric fuzes are given 
in reference 1. 

A major advantage of a photoelectric, or PE fuze, 
aside from its basic simplicity, is that the position of 
function with respect to an airborne target can be 
controlled with remarkable precision. The sensitiv- 
ity zone of a PE fuze can be restricted to a narrow 
conical zone corresponding to the latitude of maxi- 
mum fragmentation density of the missile. 

There are, however, two major limitations to a 
simple passive photoelectric fuze: (1) since the sun 
is used as a source of energy, operational use is re- 
stricted to daytime, and (2) the sun is also a target 
in the sense that if the detector of the fuze “sees” the 
sun directly, malfunction of the fuze may occur. 
These two limitations were recognized in the begin- 
ning and led to termination of the work only after 
more difficult designs (radio) had proved practicable 
for proximity operation. 

An infrared fuze would not be subject to the first 
limitation above but would be affected by the sec- 
ond. For this reason, infrared designs based on rapid, 
sensitive detectors developed by Division 16, NDRC, 
were abandoned after brief consideration. The prac- 
ticability of available radio fuzes was also a major 
factor in the abandonment. 

Several systems, which are described in the follow- 
ing chapters, were considered for eliminating the 
two major drawbacks of PE fuzes, but these were 
not fully exploited because of the success of the 
radio design. 

It is of interest to note that the only proximity 
fuze used operationally by the enemy was an active- 
type photoelectric design, developed by the Japa- 
nese. The fuze, which was used on bombs, was about 
10 times the size and weight of photoelectric fuzes 
developed by Division 4. 

27 RADIO FUZES 

In considering radio principles for proximity fuze 
operation, major consideration was given to active 
types. A passive fuze would require transmitting 
equipment as part of the fire control, which would 
increase the complexity of operational use. Although 
it was recognized that the radio method afforded ex- 


CONFIDENTTAL 


RADIO FUZES 


19 


cellent advantages in design flexibility to meet the 
requirements of various applications, there was some 
initial doubt as to the practicability of building a 
radio transmitting and receiving station into a fuze/ 
Here it is essential to state only that reliable de- 
signs were produced and that these designs 

f The technical aspects of the design and production of 
radio proximity fuzes are given in Division 4, Volume 1. 


represented solutions to most of the difficulties en- 
countered in other types of proximity fuzes. 

A major advantage of the radio method is that 
proximity operation can be obtained against any 
target which reflects radio waves. This means that a 
single basic principle can be used not only for the 
antiaircraft application but also for the variety of 
ground approach applications. 


CONFIDENTIAL 


Chapter 3 


PHOTOELECTRIC FUZE DEVELOPMENT; 
INTRODUCTION AND SUMMARY 


31 OBJECTIVES 

P hotoelectric [PE] fuzes were developed for 
use on bombs and rockets against airborne tar- 
gets. It was desired that the fuze detonate the mis- 
sile at the point on the trajectory where the greatest 
number of fragments would be directed at the target. 
The sensitivity was to be such that detonation 
would occur for all rounds which passed the targets 
within lethal range of the missile’s fragments. How- 
ever, sensitivity design for extreme range of the 
fragments proved to be incompatible with reliable 
fuze performance, and an operating sensitivity be- 
tween 50 and 100 ft was selected. Other desired 
requirements on which design considerations for the 
fuzes were based were: 

1. The fuze should be as small and rugged as pos- 
sible; 

2. It should be safe for handling and operational 
use; 

3. It should perform reliably under as wide as 
possible a range of Service conditions; 

4. It should require a minimum of special equip- 
ment and training for its operational use; 

5. It should be relatively immune to possible 
enemy countermeasures; and 

6. It should have a self-destruction feature to 
operate, in case of a miss, after passing the target. 

A number of compromises were made in require- 
ment 3 in the interests of expediency. The principle 
of operation selected restricted the operation to day- 
time use. However, it was agreed that a good day- 
time fuze available early in World War II would be 
of more value than a 24-hour fuze available probably 
one or two years later. Another compromise was in 
the selection of a power supply for the fuze. 

An ideal power supply would be required to oper- 
ate over a very wide range of temperatures and have 
unlimited shelf life. Since no such power supply was 
available, it was considered desirable to design fuzes 
around dry batteries (which begin to fail at temper- 
atures below 15 F and have limited shelf life) until 
better power supplies were developed. 

Specific projects which were undertaken were: 
battery-powered fuzes for use on (1) large bombs, 1 


(2) the British 3.25-in. UP rocket, 2 and (3) the 
4.5-in. M-8 rocket, 3 and generator-powered fuzes 
for use on bombs 4 and rockets. 3 

Since the projects were carried out in view of rec- 
ognized limitations in use, they were terminated as 
soon as more generally useful weapons (radio fuzes) 
were available and established as reliable. 

32 PRINCIPLES OF OPERATION 

The basic operating principles of all photoelectric 
fuzes developed by Division 4 are essentially the 
same. Operation can be explained simply by refer- 
ence to Figure 1. The heart of the fuze is a photo- 



Figure 1 . Block diagram illustrating operation of 
photoelectric proximity fuze. 

electric cell (photocell) which is sensitive to light 
striking its active surface. The photocell is sur- 
rounded by a lens system which restricts the light 
which the photocell can see to a relatively narrow 
zone. This zone is called the field of view. The center 
of the field of view is conical in shape, and the field 
extends only a few degrees to either side of the cen- 
ter. Light outside of the field of view has no effect 
on the photocell. When a solid object, such as an 
airplane, enters the sensitive zone (field of view) , it 
obstructs some light; consequently, the total light 
incident on the photocell is reduced. This causes a 


20 


CONFIDENTIAL 



MODELS DEVELOPED 


21 


decrease in the output current of the photocell, which 
decrease is transmitted as a signal to the amplifier. 
The amplifier increases the amplitude of the signal 
to a level sufficient to fire the thyratron when a 
predetermined minimum percentage change in light 
level occurs. The amplifier also provides signal dis- 
crimination so that very slow or extremely rapid 
changes in light intensity are not transmitted as 
signals to the thyratron. This characteristic is de- 
scribed in more detail in Chapter 4. The triggering 
of the thyratron fires an electric detonator and the 
explosive action is initiated. 

The preceding description applies only when the 
fuze is armed. Arming consists generally of three 
operations prior to which the fuze is insensitive: (1) 
application of power to the amplifier, photocell, and 
thyratron filament, usually at the time the missile is 
launched, (2) the connection of the electric detona- 
tor to the circuit and, generally at the same time, 
applying power to the thyratron plate, and (3) re- 
moval of a mechanical barrier between the detona- 
tor and booster, prior to which explosion of the 
detonator will not initiate the booster. The second 
and third operations occur at a predetermined time 
after launching. In the case of rocket fuzes, the arm- 
ing system requires a sustained acceleration, such as 
is encountered when the rocket is fired, for its opera- 
tion. 

The arming characteristics of proximity fuzes are 
very important because the fuzes are sensitive to 
external influences and may be triggered any time 
after arming. The ability of a proximity fuze to 
withstand minor influencing factors and function 
only on the target is one measure of its reliability. 

In the event that the fuze is not triggered by a 
target, usually because of passage too far away, a 
self-destruction [SD] circuit triggers the fuze at 
some predetermined time after launching. 

Further details concerning the design, operation, 
and construction of PE fuzes are given in Chap- 
ters 4 and 5. 

33 MODELS DEVELOPED 

The first PE fuze developed was a tail-mounted 
bomb fuze intended for use in bombing formations 
of enemy aircraft. Only a few such fuzes were 
built and tested. Evaluation indicated that approxi- 
mately 80 per cent of the fuzes which passed within 
about 100 ft of an airplane target could be expected 


to function properly on the target. 6 (See also Chap- 
ters 5 and 8.) a 

The project was terminated because of lack 
of tactical interest in bombing aircraft with 
bombers. 

The PE fuze on which the greatest effort was ex- 
pended was the T-4 fuze for the M-8 rocket. A 
satisfactory design was achieved for this application, 
and approximately one-third of a million units were 
procured by the Army. This fuze is pictured in Fig- 
ure 2. The fuze was designed to allow assembly with 



Figure 2. T-4 photoelectric fuze, developed for use 
on M-8 rocket. From left to right are shown: as- 
sembled fuze ready for installation in rocket; MC-380 
nose containing electronic control elements; BA-75 
battery; and SW-230 switch. Nose and switch plug 
into opposite ends of battery. 

a freshly tested battery in the field just prior to use. 
The battery and switch components of the fuze were 
identical with those used in the T-5 radio fuze. A 
full description of the electronic part of the fuze is 
given in Chapter 5. Reference is made to the radio 
volume b for a detailed discussion of the battery and 
switch. 

In acceptance tests on over 4,000 production units, 
a reliability score of 90 per cent was obtained for 
the T-4 fuze. Of the remaining 10 per cent, approxi- 
mately half were duds, and half were random func- 
tions, operating between the point of arming and the 
target'. Further details concerning the evaluation of 
the fuze are given in Chapter 8. 

None of the fuzes were used in combat because of 
a combination of reasons involving security, changes 

a Most of the work on this project was done by Section T, 
OSRD, prior to its transfer to Division 4 (then Section E) in 
the summer of 1941. 
b See Division 4, Volume 1. 


CONFIDENTIAL 


22 


PHOTOELECTRIC FUZE DEVELOPMENT 


in tactical requirements, and inadequacies of the 
M-8 rocket.® 

Following the completion of development of the 
T-4 fuze, effort was directed toward the develop- 
ment of generator-powered fuzes for use in both 
bombs and rockets. As with the T-4 and T-5 fuzes, 
power supplies were designed and developed jointly 
for use on both radio and photoelectric fuzes. The 
successful development of a wind-driven electric 
generator as a power supply for fuzes removed the 
limitations of temperature and storage of the dry 
battery. Generator development is discussed briefly 
in Chapter 5 of this volume.* Photographs of genera- 
tor-powered photoelectric fuzes for rockets and 
bombs are shown in Figures 3 and 4, respectively. 
The former was usually designated as RPEG 
(Rocket, PE, Generator), and the latter, as BPEG 
(Bomb, PE, Generator) . The BPEG was also tenta- 
tively designated by the Ordnance Department as 
the T-52 fuze. Development of these two fuzes was 
terminated before completion because of the estab- 
lished reliability of radio fuzes. 



Figure 3. Generator-powered photoelectric fuze 
[RPEG] installed in M-8 rocket. 


The production of reliable photoelectric fuzes in- 
volved extensive laboratory and field testing in order 
to evaluate performance under simulated conditions 
of operational use. Descriptions of these testing 
methods are presented in Chapters 6 and 7. A major 

c See the Administrative History of Division 4, NDRC. 
d For details of generator development, see Division 4, 
Volume 1. 


problem encountered in designing electronic devices 
for use on high-speed missiles was microphonics in- 
duced by the vibration in flight, caused by turbu- 
lence of the airstream. Development and testing 
problems were appreciably concerned with making 
due allowance for possible vibration. 



Figure 4. Generator-powered photoelectric bomb 
fuze [BPEG, or T-52]. (Bell Telephone Laboratories 
photograph.) 

Although the following five chapters (4 to 8, in- 
clusive) are concerned primarily with the T-4 fuze, 
some attention is given, particularly in Chapters 5 
and 8, to methods considered for removing some of 
the limitations of the fuze. The presentation in these 
chapters may seem somewhat detailed for a project 
now classed as obsolete, but the presentation is con- 
sidered pertinent for the following reasons. 

1. The work described represents a summary of 
technical achievement which fulfilled or exceeded 
most of the initial expectations. 


CONFIDENTIAL 


MODELS DEVELOPED 


23 


2. Intelligence reports of foreign countries indi- 
cate that photoelectric devices were investigated ex- 
tensively by other countries. Actually, the only 
proximity fuze used operationally by the enemy 
was a photoelectric fuze. Consequently, the develop- 
ment of countermeasures against possible future 
hostile fuzes can profit by having a fairly complete 
record of our own experience with photoelectric 
ordnance devices. 

3. Some of the techniques and components de- 
veloped may have other applications, either of peace- 


time or military nature. Actually, the photoelectric 
cell developed for the fuze has already found other 
applications. 6 

4. According to postwar plans of the Army Ord- 
nance Department, optical fuze methods will be 
reinvestigated to determine ways and means of re- 
moving limitations or developing other applications. 
Consequently, this record should be of value as a 
starting point in such a survey. 

e See Division 4, Volume 2, Chapter 8. 


CONFIDENTIAL 


Chapter 4 


BASIC PRINCIPLES AND DESIGN OF PE FUZES 3 


4.1 INTRODUCTION 

T his chapter deals largely with those aspects of 
photoelectric [PE] fuze design which involve 
the interaction of the fuze with its target. Other 
general principles of the fuze design, such as mechan- 
ical problems of stability and ruggedness and elec- 
tric power supply problems, are essentially the same 
as for the radio fuzes. b 

PE fuzes were designed primarily for use against 
airborne targets. An ideal proximity fuze for this 
application would have the following characteristics. 

1. It would detonate all projectiles which pass 
close enough to the target to cause appreciable 
damage. 

2. The detonation would occur at the point on the 
trajectory of the missile where the explosion would 
inflict the greatest damage. 

The PE fuze can be designed to meet both re- 
quirements under normal daylight conditions and 
some restriction on trajectory orientation with re- 
spect to the sun. The fuze is essentially a simple 
photoelectric triggering device. The proper burst 
point is obtained by restricting the light on the 
photocell to the direction which coincides with the 
maximum density of fragmentation. 

Attainment of the above ideal operating charac- 
teristics may be considered to be the basic design 
problem of the fuze. The first involves the sensi- 
tivity requirements and the second the “look- 
forward angle.” 

Sensitivity is expressed either as the maximum 
distance of passage from a specified target at which 
the fuze operates (radius of action) , or as the mini- 
mum percentage light change (threshold) on which 
the fuze operates. The main design problems are 
met in analysis of sensitivity requirements and de- 
sign of circuits most suited to meet them. Proper 
design involves study of the interrelation of lighting 
conditions, target characteristics, photocell and 
amplifier properties, and other factors. The sensi- 

a This chapter was written by Alex Orden of the Ordnance 
Development Division of the National Bureau of Standards 
and by Corporal R. F. Morrison of the VT detachment of 
the Army Ordnance Department. 
b See Division 4, Volume 1. 


tivity characteristics of the fuze are governed by 
the following considerations. 

1. There is an optimum design sensitivity which 
will give maximum fuze effectiveness. If the fuze 
were too sensitive, the increased percentage of fuzes 
which would detonate on passing the target would 
be outweighed by a decrease of fuze reliability. 

2. The fuze must have approximately the same 
sensitivity over a wide range of light levels. This 
requires design of a circuit to convert the linear re- 
sponse of the photocell (proportional to the magni- 
tude of the light change) to a logarithmic response 
(proportional to the percentage change in light) . 

3. The fuze must operate on an abrupt change of 
light. The circuit must be designed to be most sensi- 
tive to light changes at rates obtained when ap- 
proaching or passing targets and less sensitive to 
extraneous signals from clouds or the ground. 

4.2 DESIGN PRINCIPLES 

421 Look-Forward Angle 

The field of view of the photocell must have radial 
symmetry with respect to the axis of the fuze in 
order that the fuze may see the target at any aspect 
of passage. 

The center of the field of view should be a cone 
corresponding to the direction of most intense frag- 
mentation of the projectile. The look- forward angle 
is defined as the angle between the normal to the 
projectile axis and the center of the field of view 
(Figure 1). Look-forward angles on various models 
ranged from about 0 to 25 degrees. The look-forward 
angle is selected on the assumption that the center 
of the field of view is in the direction of maximum 
fragmentation of the projectile. 

In considering the relation between the target 
signal and the time of detonation, experiments have 
shown that delays in the detonator and explosive 
train are negligible.® The time lag in the explosive 
train is of the order of 0.001 sec, which represents 
not more than 2 ft of travel of projectiles of the type 
for which PE fuzes were designed. 

The direction of maximum fragmentation, i.e., the 

c See Division 4, Volume 1, Chapter 3. 


CONFIDENT I VI. 


24 


DESIGN PRINCIPLES 


25 


desired look-forward angle, can be determined for 
any proposed tactical application by vector addition 
of the velocity of the fuze relative to the target and 
the mean velocity of fragments from a projectile 



exploded at rest. It is usually adequate to assume 
that the mean direction of fragmentation from a 
stationary explosion is normal to the axis of the pro- 
jectile. Therefore, the look-forward angle should be 


stationary explosion with a range of velocities of 
2,000 to 6,000 ft per sec. When combined with a 
vehicle velocity of 1,000 ft per sec, the fragment 
spray would spread into a zone 9.5 to 26.5 degrees 
forward from the normal. 

When reliable data on stationary fragmentation 
velocity distribution are available, it is desirable to 
use the true direction of maximum fragment density 
rather than assume that it is normal to the projectile 
axis. 9>ld At the time of development of the T-4 fuze 
and earlier photoelectric fuzes, the data were rather 
meager. In particular, the M-8 rocket, for which 
the T-5 fuze was intended, was developed concur- 
rently with the fuze. On the basis of predicted per- 
formance, a look-forward angle of 22.5 degrees was 
selected. It was subsequently shown 8>9 that a look- 
forward angle of about 0 to 5 degrees would have 
been better. 41 

4 2 2 Field of View 


6 — arc tan 

where 

V r = velocity of fuze relative to target and 
T / =mean stationary fragmentation velocity. 


A typical example is: velocity of fuze relative to 
target in plane-to-plane pursuit firing with rockets 
is 1,000 ft per sec; mean velocity of fragments 
from stationary explosion is 3,000 ft per sec; there- 
fore, the required look-forward angle is tan -1 
(1,000/3,000) = 18.5 degrees. 

The possibility of other tactical applications must 
be considered, and it may be desirable to select a 
compromise value for the look-forward angle. In the 
above example, a typical velocity of fuze relative 
to target for head-on plane-to-plane firing would 
be 1,600 ft per sec, which would require a look- 
forward angle of 28 degrees. Considering the size 
of targets and the angular spread in the fragment 
distribution, the look-forward angle may not be 
critical, a value selected for one tactical application 
being fairly effective in other applications. The 
spread in angular distribution of fragments from a 
projectile in motion is considerably greater than 
that for a stationary explosion, since the range of 
velocities of the fragments combined vectorially 
with projectile velocity spreads the angular cover- 
age. For example, consider fragments concentrated 
in the direction normal to the projectile axis in a 


For design analysis the field of view (Figure 1) 
is represented by a lens transmission curve as shown 
in Figure 2. The angle between the 50 per cent 



54321012345 

DEGREES 

Figure 2. Lens transmission curve. 


transmission points is frequently used as the param- 
eter defining the field of view. This angle represents 
the width of an equivalent rectangular transmission 
d See Division 4, Volume 1, Chapter 1. 


CONFIDENTIAL 


26 


BASIC PRINCIPLES AND DESIGN OF PE FUZES 


curve, which would transmit approximately equal 
light flux. 

The width of the transmission curve is controlled 
by the width of the slit between the lens and the 
photocell. The sharpness of cutoff is limited by lens 
aberrations. 

The width and the cutoff slope of the transmission 
curve have considerable bearing on target pulse 
shapes, radius of action, susceptibility of the fuze 
to sunfiring, and response to stray optical disturb- 
ances. The shape of the lens transmission curve has 
been used in calculations in which the response of a 
fuze to a specified target was determined by analyti- 
cal means. 4 * 6 However, no studies have been made to 
determine optimum lens transmission characteris- 
tics. Designs have been based on the following gen- 
eral considerations. 

1. The width of the field of view should be equal 
to or less than the smallest angle subtended at the 
fuze by targets on which the fuze is expected to 
operate, i.e., the angle subtended by typical targets 
at a distance equal to the desired radius of action. 
With this design the target signal falls off inversely 
as the first power of the distance within the radius 
of action. At greater distances of passage, the target 
signal falls off inversely as the square of the dis- 
tance, and the target signal rapidly becomes less 
effective. 

2. A narrow field of view and a sharp cutoff ap- 
pear to offer the simplest approach to reducing sun- 
firing and firing on extraneous light signals to a 
minimum for fuzes of standard design, i.e., not in- 
cluding the various experimental designs intended 
to eliminate sunfiring. The narrower the field of 
view, the less likely that the fuze will see the sun. 

The ability of the fuze to discriminate between 
true targets and extraneous slower light changes de- 
pends on the selectivity of the amplifier for abrupt 
signals. Since the slope of the lens transmission 
curve affects the light signal from both true targets 
and extraneous light changes in the same sense, the 
slope of the transmission curve may not be critical, 
provided the lens and amplifier characteristics are 
properly matched. 

3. Too narrow a field of view would result in loss 
of sensitivity at low light levels. 

4 2 3 Radius of Action 

The radius of action [ROA] of a given fuze model 

depends on target characteristics, lighting condi- 


tions, aspect at which the fuze sees the target, and 
velocity of the fuze relative to the target. For devel- 
opment and analysis purposes, it is desirable to 
establish standard field test conditions and a stand- 
ard target. The radius of action under these condi- 
tions serves as a measure of fuze sensitivity and may 
be referred to as ROA sensitivity. Similarly, the 
minimum light change on which fuzes operate under 
specified laboratory test conditions provides a 
standardized measure of sensitivity, which is called 
the threshold sensitivity . The relation between ROA 
sensitivity and threshold sensitivity depends on the 
relative response of the particular fuze model to 
light pulses from targets. 6 

For analytical purposes, the radius of action is 
generally considered to define a zone within which all 
fuzes function and outside of which none function. 



Figure 3. Per cent of fuzes operating on target versus 
radius of passage. (T-4 fuzes on 3 x /4-in. practice 
rockets fired against 12-ft diameter black balloon 
target.) 

Statistical variation encountered in practice is 
shown in Figure 3. The distribution curve of per 
cent proper function is based on the firing of ap- 
proximately 200 rounds of pilot production T-4 
fuzes against a 12-ft diameter black balloon at Fort 
Fisher Proving Ground. (See Chapter 7.) The re- 
sults indicate that the radius of action on individual 
rounds varied from 50 to 125 ft. The spread may be 
attributed in part to variation of internal fuze char- 
acteristics and in part to day-to-day variation of 
firing conditions, such as cloud conditions and tar- 
get elevation. 

In principle, there is an optimum ROA for which 
the fuze should be designed in order to make it most 
effective for a given application. The optimum 
value could be determined in advance as a basis for 
production design if experimental data were ob- 


s 


CONFIDENTIAL 




DESIGN PRINCIPLES 


27 



•Figure 4. Probability of serious damage to SB2A airplane by 5-in. rocket shell. Figure on each curve is 
damage probability for points on that curve. 


tained on: (1) damage probability as a function of 
distance of passage for projectile bursts 4 > 8 — as in 
Figure 4, and (2) fuze reliability as a function of 
ROA sensitivity — as in Figure 5. (Note that Fig- 
ure 5 differs from Figure 3. Figure 3 shows statisti- 
cal spread in sensitivity of fuzes of a particular 
design sensitivity; Figure 5 shows expected loss of 
fuze reliability due to increase of malfunctions with 
increase of design sensitivity.) 

On the basis of data of the type shown in Fig- 


ures 4 and 5 the determination of optimum design 
ROA is as follows: (1) The cumulative damage 
probability curve is obtained by integration of the 
conditional probabilities under the expected condi- 
tions of projectile dispersion and burst positions — see 
Figure 6. (2) The product of burst effectiveness 
(Figure 6) by reliability (Figure 5) then gives the 
overall probable damage as a function of design 
ROA — see Figure 7. This curve shows a maximum 
damage probability at the optimum design ROA. 


CONFIDENTIAL 


28 


BASIC PRINCIPLES AND DESIGN OF PE FUZES 



RADIUS OF ACTION (FEET) 

Figure 5. Fuze reliability versus fuze sensitivity 
(ROA). (Hypothetical curve used to illustrate design 
considerations given in text.) 

The above procedure is applicable in principle 
but would require extensive advanced engineering 
and tactical information. It has been presented pri- 
marily in order to bring out basic considerations 



RADIUS OF ACTION (FEET) 

Figure 6. Cumulative probability that target air- 
plane will be incapacitated by single rocket as func- 
tion of fuze ROA. This curve is calculated on basis 
of Figure 4 undei following assumptions: (1) rocket 
dispersion = 15 mils, (2) range = 1,000 yd, (3) fuzes 
function at look-forward angle of 30°, (4) for any 
ROA, all rounds which pass within ROA function 
against target and all rounds which pass outside ROA 
do not function. 

with regard to the ROA. In the development of the 
T-4 the ROA requirement was based on the nomi- 
nal lethal radius of the vehicle. The M-8 4.5-in. 
rocket was assumed to have a lethal radius of 60 ft. 
During the development of the fuze, it was field 


tested against a 12-ft diameter black balloon and 
required to produce a high proportion of target 
bursts on rounds passing within 60 ft of the target. 
Presumably, after the pilot design had demonstrated 
the required sensitivity, development of units of 
higher sensitivity would have been in order. In the 
case of the T-4 fuze, however, this was not done 
because of the urgency of getting a model into pro- 
duction. Moreover, an increase of sensitivity would 
have required a major design change, involving an 
increase in the number of stages of amplification. 



Figure 7. Overall probability of serious damage 
versus fuze sensitivity. This curve combines damage 
probability (Figure 6) with fuze reliability (Figure 5). 

It indicates that, under conditions of Figures 4. 5, 
and 6, a fuze designed to have ROA of 70 ft would 
have greatest effectiveness. 

4 2 4 Target Analysis 

Description of Light Conditions 

The magnitude of the light change due to a target 
depends on the brightness of the side of the target 
toward the fuze, relative to the background. When 
the fuze passes a target at any aspect at which the 
line of sight toward the target is above the horizon, 
the background of blue sky or of clouds is ordinarily 
brighter than the target, and the photocell receives 
a negative pulse. When the line of sight is below the 
horizon, the ground background may be lighter or 
darker than the target at low altitude, while with 
increasing altitude the background brightness in- 
creases because of light scattering by the atmos- 
phere below. Thus the target pulse is generally nega- 
tive, and the fuze circuit is designed accordingly. 

As a first approximation to the characteristics of 
the target pulse, it may be said that the target ob- 


CONFIDENTIAL 



DESIGN PRINCIPLES 


29 


scures a fraction of the background light, and that, 
under given conditions of target shape, passage dis- 
tance, etc., the fraction obscured is independent of 
the general light level. For this reason the fuze sen- 
sitivity is best measured in terms of per cent light 
change. 

Discrimination of Target Signals from 
Background Light Changes 

The principal limitations on fuze sensitivity are 
optical disturbances in the background and electri- 
cal disturbances within the fuze (noise and micro- 
phonics). The optical disturbances are mainly 
clouds, the horizon line, and nonuniform terrain. 
The percentage light change caused by these dis- 
turbances may be considerably greater than that 
which is due to a target. However, the rate of change 
of light due to a proper target is more rapid. Analy- 
sis of target characteristics permits design of an 
amplifier which is much more sensitive to pulses 
received from targets than to the slower pulses 
received from background variations. 

The relative response to a near-by target and to 
background light changes depends also on the spec- 
tral response of the photocell. Scattering of light by 
the atmosphere increases as the wavelength de- 
creases ; therefore, the background generally appears 
more uniform to a photocell, whose response is 
largely in the short-wavelength region of the visible 
spectrum. 

Light Measurement 

The photometry involved in the fuze development, 

i.e., the measurement of light level and change of 
light, is most easily accomplished by using the fuze 
optical system and photocell as a light receiver and 
measuring the light in terms of microamperes of 
photocell current. Such data can be converted to 
light flux by calibration of the photocell in terms of 
microamperes per lumen. 

Target Signal 

The radius of action depends on many factors 
external to the fuze: shape, size, and reflection char- 
acteristics of the target, altitude, and atmospheric 
conditions. As a basis for analysis of the relation 
of any of these factors to fuze design, it is desirable 
to determine the curve of per cent light change vs 
time for fuzes passing targets under various sets of 
conditions. 


Target pulse curves have been obtained by the 
following methods. 

1. Flyover tests. The fuze was set on the ground, 
and the photocell current was recorded while a typi- 
cal target airplane was flown over it. The time scale 
of the curve can readily be converted to correspond 
with any projectile velocity. 

2. Simulated target. A small-scale model of a 
target was moved across a bright surface back- 
ground to determine the pulse curve experimentally 
in the laboratory. 

3. Computation. The shape of the target pulse 
was computed on the basis of the size and shape of 
the target and the transmission curve of the fuze 
lens. This method was used to obtain the pulse 
curves of the 12-ft target balloon, as shown in Fig- 
ure 8. 


- 


/T 
/ / 







- 

R=49‘ / 

T * 

f / 

/ 

/ 







- 

/ / 

/ 

^ R=69^ 








/ / 

/ / 

/ / 








- 

// / 

/ / / 

V / 








1 



S 






- V 
// / 

s/ 


R=I72^ 






ft r 

J A' 

/ / 

f 



R*34 4* . 

1 






0 1 2 3 4 5 6 7 8 9 10 II 12 13 14 15 16 17 

MILLISECONDS 


Figure 8. Target pulses from 12-ft diameter spherical 
target at various radii of passage ( R ). (Projectile 
velocity — 1,500 ft per second.) 

Since it is not practical to consider the detailed 
relation of all external variables to fuze design, it 
is desirable to establish a simple standard target for 
development field testing and analysis. The pulse 
from this target should be representative of that 
expected from combat targets. A black balloon 12 ft 
in diameter was used for a large part of the T-4 
development. 

The radius of action against the standard target 
is established by field tests. This provides a basis 
for judging qualitatively whether the fuze sensitiv- 


CONFIDENTIAL 


30 


BASIC PRINCIPLES AND DESIGN OF PE FUZES 


ity is adequate for expected combat targets and fir- 
ing conditions. 

The light threshold, or minimum per cent light 
change, on which the fuze will function depends on 
the shape of the target pulse. It is convenient to use 
a step pulse (instantaneous light change) for labora- 
tory development experiments on fuze thresholds. 
(For production control testing, the threshold on 
a 60-c alternating light signal is most useful.) 


output.) Figure 8, showing the target signal from 
a 12-ft balloon, gives slant pulse times of approxi- 
mately 5 to 10 milliseconds for passage distances 
of 49 to 172 ft. For this range of pulse times, T-4 
thresholds are 1.5 to 3 times greater than for a step 
pulse. 

4 2 5 Light Level Variation 


Threshold Sensitivity 

The threshold sensitivity of a fuze is ordinarily 
given for a step pulse light signal. The threshold 
against actual targets varies with the duration and 
shape of the pulse. As an approximation, a target 
pulse may be considered as a linear decrease in light 
from the beginning of the light change to the instant 
of maximum obscuration (slant pulse). For an am- 
plifier of the type used in the T-4, the threshold 
rises as the slant pulse time increases. 

The relation between the threshold of a fuze on 
a step pulse and its threshold against a given tar- 
get in the field may be computed by calculations 


















> 

7 





V " s 

rEP" p 

ULSE 


W 

SLi 

— T — * 
NT PU 

.SE 









































































2 4 6 8 10 12 14 16 18 20 

T (MILLISECONDS) 


Figure 9. Amplifier output on slant pulse input 
signal of duration T relative to output on step pulse. 
Slant pulses serve as approximation to target obscura- 
tion signals. 

using Heaviside operational calculus. 6 The relative 
output of a T-4 amplifier for slant pulses of vary- 
ing duration is shown in Figure 9. (The threshold 
is inversely proportional to the relative amplifier 


The light level, or total light flux on the photocell, 
varies with time of day, altitude, cloud and terrain 
conditions, and other factors. Since the change in 
light due to a target is approximately proportional 
to the light level, the radius of action against a 
given target can be kept approximately independent 
of light level by designing the fuze circuit to respond 
to the per cent change in light. There are many 
types of circuit whose response is sufficiently close 
to a percentage response for use in the photoelectric 
fuze. 1 The simplest of these is one using a nonlinear 
resistor (varistor or thyrite unit) as the photocell 
load resistor, as in the T-4 fuze. 

Variation of light level with ambient conditions 
is shown in Figures 10, 11, and 12. Figure 10 3 shows 
the relative current of a photocell of the type used 
in the T-4 fuze over the course of a day. A rain- 
storm occurred at the time of the deep trough in the 
curve in the early afternoon. Figure 11 shows the 
variation of light level with time of day averaged 
over a week. Figure 12 5 shows the variation of light 
level with altitude, obtained with a photocell car- 
ried in an airplane. The relative responses with the 
photocell directed upward toward the horizon and 
downward toward ground and water are shown. 

In order to cover the range of light levels gen- 
erally encountered, the fuze should ideally have con- 
stant sensitivity to percentage changes in light over 
a range of light levels of at least 50 to 1, e.g., from 
about 0.5 microampere to 25 microamperes photo- 
cell current in a T-4 fuze. A design which meets this 
requirement can provide satisfactory operation 
from about 15 minutes after sunrise to 15 minutes 
before sunset. The rate of change of light level near 
sunrise and sunset is quite rapid; therefore, the low 
light level limit of adequate fuze sensitivity is not 
critical, since a change of fuze design, which extends 
the sensitivity to lower light levels, adds only a few 
minutes to the available operating time. 

Circuits which have the required percentage re- 
sponse characteristic may be said to have a logarith- 


CONFIDENTIAL 


DESIGN PRINCIPLES 


31 



Figure 10. Relative light level seen by photocell ofT-4 fuze during course of a day. (Rain between 2:00 and 3:00 p.m.) 

mic response feature in the photocell circuit, or in 
the input element to the amplifier, or in the overall 
photocell and amplifier circuit. For example, if the 
photocell circuit is to be designed to provide a cur- 
cent change which is proportional to per cent light 
change we have 

.. dL 

di o c -jjj 


and 

i = KlogL, 

where oc indicates “proportional to,” i is photocell 
current, L is light flux, and K is a constant. 

Thus the current in the photocell circuit must be 
proportional to the logarithm of the light level. 

Alternatively, the photocell response may be 
linear, and the percentage response may be pro- 



Figure 11. Variation of relative light level with time of day averaged over a week. 




CONFIDENTIAL 


32 


BASIC PRINCIPLES AND DESIGN OF PE FUZES 



Figure 12. Variation of relative light level (seen by 
photocell) with altitude. 


vided by the voltage input to the amplifier; i.e., the 
following relationships are required (v is amplifier 
input voltage). 

i oc L, 
di oc dL, 
j. , di dL 

av oc — oc — , 

i L 
v = K log L. 

Thus in this case the voltage across the amplifier 
input is to be proportional to the logarithm of the 
light level. 

4-3 BASIC DESIGN 

The operation of the photoelectric fuze may be 
divided into three parts: arming; functioning on a 
target; and, in the absence of a target within firing 
range, self-destruction. 

The arming mechanism delays the arming of the 
fuze so that the projectile is unable to explode until 
it has traveled a safe distance from the launching 
vehicle. 


The self-destruction feature sets off the fuze after 
a given time, in case the projectile does not come 
within operating range of a target. This feature 
keeps live ammunition from falling on friendly ter- 
ritory and prevents capture of the fuze by the 
enemy when it is used over enemy territory. It is 
also useful for testing operation of the fuze in de- 
velopment work. 

4,31 Mechanical Design 

The fuze must be of small size and weight so that 
it does not take up a disproportionate share of the 
projectile. Since it is mounted at the front of the 
projectile, its shape must be such that it does not 
detract from the ballistic properties of the projectile. 

The photocell should be mounted as far forward 
as possible so that the lens will support the least 
weight, and the amplifier is mounted next to it so 
as to keep the leads to the photocell as short as 
possible. The arming mechanism should be placed 
to the rear because it contains the electric detonator, 
leaving the battery between the amplifier and the 
switch. 

For convenience in manufacture and testing, the 
T-4 fuze was made in the form of subassemblies 
which could be assembled just before use. These sub- 
assemblies were: photocell-amplifier unit, battery 
and thyratron-firing condenser unit, and switch- 
detonator unit. Testing immediately before use was 
especially desirable in the case of the dry cell bat- 
tery, which suffers rapid deterioration in some 
climates. 

The components and final assembly of the fuze 
must be rugged so as to withstand the acceleration 
to which the fuze is subjected. Vacuum tube ele- 
ments must be so mounted that vibrations which 
might produce signals within the passband of the 
amplifier are of very small amplitude. Amplifier 
components are mounted on a bakelite plate and the 
amplifier cavity is filled with a potting compound 
such as ceresin wax having good electrical insulating 
properties. This holds the components rigidly in 
place. The wax serves the additional function of 
moistureproofing the unit. 

Some means of delayed arming must be provided 
as a safety feature to prevent premature explosions. 
The switch of the T-4 fuze incorporated a number 
of safety measures: the plate and filament supply 
circuits were kept open before firing, while the 


CONFJDKNTIAL 


BASIC DESIGN 


33 


detonator leads were shorted and a metal plate was 
kept between the detonator and the booster. 

The switch was operated by the acceleration of 
the rocket and was so designed that it could not be 
set off by accidental jars due to dropping, etc. The 
acceleration closed the A and B circuits immedi- 
ately upon firing. About 0.5 second later the arming 
was completed by connecting the detonator into the 
plate circuit of the thyratron and sliding the metal 
plate over to provide an opening through which the 
explosion of the detonator could reach the booster. 

4,3,2 Optical Design 

The optical system of the T-4 fuze was designed 
to see a ring of sky about 5 degrees wide and 20 
to 25 degrees forward of the equatorial plane of the 
projectile. This width was about equal to the mini- 
mum angular width of the target at the lethal range 



Figure 13. Optical system of T-4 fuze (simplified). 


of the shell, and the direction was determined by 
the expected fragmentation cone of the M-8 rocket. 
The optical system consisted of a toroidal lens set in 
the outer* case of the fuze and a ring slit surround- 
ing a photocell at the axis of the fuze. (See Fig- 
ure 13.) 

The lenses were made of Lucite or Plexiglas and 
formed either by machining a plate of Lucite to the 
required shape or by molding the plastic and 
machining only the optical surfaces. 

Since the smaller radius of curvature of the toroid 
was small compared with the larger radius, the focal 
properties of the toroid were approximately those 
of a cylindrical plano-convex lens. The image of a 
distant point of light was a line in the case of a 
cylindrical lens, and for the toroid it was roughly 


the arc of a circle of radius equal to the larger 
radius of the toroid. 

To find the radius of curvature, it was convenient 
first to compute the focal length of a lens of unit 
radius and of the proper relative width and thick- 
ness for refractive index 1.49. The required radius 
of curvature was then the desired focal length 
divided by the focal length for unit radius. The lens 
was made as wide as possible without introducing 
serious aberrations. This width was approximately 
1.2 times the radius of curvature. The optimum 
focal length of such a lens was less than that of a 
narrow lens. For a narrow lens of unit radius and 
of thickness equal to the radius, the unit focal length 
was 2.37 cm, whereas for the wide lens it was 2.20 
cm. lc 

The slit which was placed at the principal focus 
of the lens was made in a number of ways. One 
method was to bring the light to a focus at the sur- 
face of the lens block or the photocell wall. The lens 
surface or photocell wall was then painted black 
and the paint cut away to form the slit. An alternate 
method made use of opaque sleeves placed over 
opposite ends of the photocell and so spaced as to 
form a slit. 

The position of the slit along the axis of the fuze 
controlled the look-forward angle of the fuze, and 
the slit width controlled the angular width of the 
ring of sky seen by the fuze. 

The earlier models of the photoelectric fuze uti- 
lized photocells with conical cathodes, whereas the 
later models used photocells with flat cathodes. The 
flat cathode enabled light from the area seen by the 
fuze to spread evenly over the entire cathode sur- 
face. This smoothed out inequalities in the emission 
from various parts of the cathode and provided a 
more uniform response to light from various direc- 
tions. 2 

4,3,3 Electrical Design 

The electrical design of the PE fuze may be 
divided into four subcircuits which may be desig- 
nated as (1) the input circuit, (2) amplifier, (3) 
firing circuit, and (4) self-destruction [SD] circuit. 

Input Circuit 

The input circuit design must involve a means of 
coupling the amplifier to the high-impedance photo- 
cell circuit as well as provide a logarithmic response 
so that the amplifier will respond to a certain per- 


CONF1DENTIAL 


34 


BASIC PRINCIPLES AND DESIGN OF PE FUZES 


centage change of light intensity regardless of the 
general light level. These requirements can be met 
by use of various nonlinear impedances, such as 
vacuum tubes operating over the curved portion of 
their characteristic, or by resistive materials, such 
as thyrite, whose impedance depends upon current 
density. la 

Early models of the photoelectric fuze made use 
of a vacuum tube connected so that the photocell 
current flowed between the grid and cathode of the 
tube. With this arrangement, larger currents re- 
sulted in lower grid-cathode impedance and, hence, 
lower gain. This model used three stages of ampli- 
fication. 

In later models (T— 4) , use was made of thyrite 
resistors, whose impedance varies inversely with 
current density. The use of the thyrite resistor and 
adoption of the single-stage amplifier simplified the 
unit considerably. Some difficulty was experienced 
due to the high-impedance grid resistor (90 meg- 
ohms) used with this amplifier. Development of 
photocells of higher sensitivity made it possible to 
reduce this to a lower value. 

Amplifier 

The type of amplifier to be used depends upon a 
number of factors. The frequency characteristic of 
the amplifier must be such that the frequencies pre- 
dominantly present in the electric pulse generated 


in the photocell by the passage of the projectile past 
the target will be amplified, and no others. 

Since the current in the photocell is proportional 
to the light falling upon it, the pulse shape will be 
determined by the rate at which light is cut off from 
the cell and will be different for different aspects 
of the target. A careful analysis shows that these 
differences are important only when close to the 
limit of sensitivity. In no case is the light cut off 
very abruptly. The shape of the later stages of the 
pulse is not of particular importance since the ini- 
tial stages will nearly always fire the unit in actual 
use. There is a gradual diminution in the light as the 
target passes into the field of view. Therefore, as a 
first approximation, the time required for the change 
from full illumination to the illumination with the 
target in the field of view is taken to be one quarter 
period of the strongest frequency in the pulse. 

Since the relative velocity as well as the separa- 
tion of the missile and target may differ with each 
round, the frequency of the pulse will not be a con- 
stant. A shaped amplifier with maximum gain at 100 c 
and 50 per cent of maximum gain at 30 and 800 c 
proved satisfactory in the T-4 fuze. Variations in 
light level and noise, due to the low-frequency yaw 
of the projectile as well as high-frequency vacuum 
tube microphonics, were greatly reduced by this 
shaping. 

The gain of the amplifier was sufficient to give 



CONFIDENTIAL 


BASIC DESIGN 


35 


an output of about 4 volts for a 1 per cent light 
change in the photocell illumination. The photocell- 
varistor combination generally used in the T-4 fuze 
gave a voltage output of about 0.1 volt per 1 per 
cent change in light intensity, which indicated that 
a voltage gain in the amplifier of about 40 was neces- 
sary. 

The gain vs frequency curve for the T-4 amplifier 
is shown in Figure 14, while the amplifier circuit 
diagram is shown in Figure 15. The condensers C sg , 
C p and C c provide the low-frequency cutoff, while 
C p determines the high-frequency cutoff. 

The peak frequency gain of about 40 obtained 
with this amplifier was near the maximum that 
could be obtained in a single stage without the use 
of regenerative feedback. 

Firing Circuit 

The main elements of the firing circuit were the 
thyratron and the squib, or electric detonator. The 
thyratron was furnished with negative grid bias 
about 4 volts in excess of that necessary to prevent 
firing. The amplifier output was coupled to the thy- 
ratron grid through a condenser. An output pulse 
(from the amplifier) of greater magnitude than 4 


PENTODE THYRATRON 



Figure 15. Circuit diagram of T-4 amplifier. 

volts would, therefore, cause the thyratron to fire. 
The detonator was connected in the plate circuit of 
the thyratron and carried the plate current of the 
thyratron, which, when triggered, was large enough 
to cause explosion of the squib. 


Self-Destruction 

A self-destruction feature was incorporated in the 
fuze to prevent capture of duds by the enemy and to 
prevent damage to ground forces when used over 
friendly territory. A time of approximately 10 sec 
was required. 

The self-destruction circuit of the T-4 fuze con- 
sisted of a condenser, which was slowly charged 
through a high resistance until it discharged through 
a neon lamp. The voltage drop across a resistor in 
series with the neon lamp was used to pulse either 
the amplifier or the thyratron. 6 

Difficulties due to inconsistent breakdown voltages 
of the neon lamps were eliminated by using lamps 
containing small amounts of radioactive material. 

4 ‘ 3 * 4 Power Supply 

The power requirements of the T-4 photoelectric 
fuze were moderate, and, in fact, appreciably less 
than for the T-5 radio fuze. Batteries which had 
deteriorated so that they were below tolerance for 
the T-5 fuze could be used for T-4 fuzes. 

The electronic circuits required a high-voltage 
plate supply, a filament supply, and a grid bias 
voltage. 

A plate supply voltage of 138 volts was found 
sufficient to supply the photocell and amplifier as 
well as the thyratron. The steady current drain was 
small, less than 300 microamperes for the photocell 
and amplifier. A large current pulse, however, was 
required to fire the detonator. This requirement was 
met by using the discharge of a capacitor through 
the thyratron to fire the detonator. 6 A capacitor 
of 1.6 microfarads was built into the power supply 
for this purpose. 

The tubes used required a filament supply voltage 
of 1.5 volts. The current drain was less than 200 
milliamperes for the T-4 fuze. 

A grid bias voltage of at least 6 volts was required 
for the thyratron, and a bias of 1 or 2 volts for the 
amplifier, depending upon the type of pentode used. 

e See Division 4, Volume 1, Chapter 3. 


CONFIDENTIAL 


Chapter 5 

DESCRIPTION OF PHOTOELECTRIC FUZE TYPES 


s-i INTRODUCTION 

A ll photoelectric [PE] fuzes developed by 
- Division 4 operated on the same basic principle 
and followed the same general electrical design. The 
method of operation and general procedure for de- 
sign have been described in Chapters 3 and 4. The 
major differences in the various models were in 
mechanical layout and assembly, and in the method 
of arming, as required by the properties of the mis- 
siles for which they were intended. There were also 
differences in the method of obtaining the so-called 
logarithm characteristic and in the properties of the 
electrical components. The logarithm characteristic, 
as described in Chapter 4, insured uniform sensitiv- 
ity at various levels of light intensity. 

Models were developed for four different sets of 
military requirements. However, all these were for 
antiaircraft use. These models were, in order of 
development: 

1. Model C, a tail-mounted bomb fuze for air- 
to-air bombing; 

2. Model BR, or Mark 1 (Ordnance designation) , 
a nose-mounted rocket fuze for the 3.25-in. British 
antiaircraft rocket; 

3. T-4, a nose-mounted fuze for the 4.5-in. M-8 
rocket intended for air-to-air operation ; 

4. BPEG, or T-52 (Ordnance designation), a 
nose-mounted bomb fuze for air-to-air bombing, 
primarily in connection with toss bombing. b 

There were also several interim or developmental 
models 1 - 3 - 104 preceding each of the four listed above. 
Of the four models listed, only the T-4 fuze was 
produced in quantity. The Army procured approxi- 
mately a third of a million T-4 fuzes, with four 
manufacturers participating in the production pro- 
gram. 

The Bomb, PE, Generator fuze [BPEG] was prac- 
tically ready for production release at the time work 
on photoelectric fuzes was terminated. 

The Model C and BR fuzes are described in Sec- 
tion 5.2, the T-4 in Section 5.3, and the BPEG fuze 

a This chapter was written by Charles Ravitsky, T. M. 
Marion, W. E. Armstrong, and J. G. Reid, Jr., all of the 
Ordnance Development Division of the National Bureau of 
Standards. 

b See Division 4. Volume 2. 


36 


in Section 5.4. Also described in Section 5.4 are sev- 
eral experimental models developed to improve the 
usefulness of the photoelectric method in general 
and the T-4 fuze in particular. The important prop- 
erties of the photocells developed for the PE fuzes 
are described in Section 5.5. 

Methods and results of testing and evaluating the 
fuzes are covered in Chapters 6, 7, and 8. 

32 EARLY PE FUZES 

5 21 Model C Fuze 1 ' 3104 

General. A photograph of the Model C fuze is 
shown in Figure 1 and a circuit diagram of the elec- 
tronic assembly in Figure 2. The fuze was assembled 
in a steel tube 3.25 in. in diameter and 12 in. long. 
The tube was clamped in an adapter which, in turn, 
was screwed to the rear of the bomb, replacing the 
fin-locking nut. These fuzes were tested only on 
inert-loaded bombs, using spotting charges, and for 
this purpose the electric detonator was attached 
exterior to the fuze. The project was terminated prior 
to the development of a high-explosive detonating 
system. A detailed description of the Model C fuze 
may be found in reference 1. 

Optical System. A toroidal lens 1 made of Lucite 
provided a conical field of view centered 80 degrees 
back from the forward axis of the bomb. (Look- 
forward angle of 10 degrees, see Figure 1, Chap- 
ter 4.) The width of the field of view (defined in 
Chapter 4) was 2 degrees. The photocell was a 
vacuum-type, blue-sensitive cell. 

Amplifier. The input stage 1<3 of a three-stage 
amplifier provided a variable load resistance for this 
photocell. When connected as shown in Figure 2, the 
input impedance of the first tube decreased as the 
photocell current increased. This characteristic in- 
sured that, at various light levels, a given percentage 
change in light level incident on the photocell would 
give a signal of reasonably constant magnitude. The 
resistors and capacitors of the amplifier were chosen 
to give a peak gain at about 20 c. The overall sensi- 
tivity was such that a decrease of about 0.5 per cent 
in the light incident on the photocell would trigger 
the thyratron. Actually, the sensitivity varied from 


CONFIDENTIAL 


EARLY PE FUZES 


37 



Figure 1 . Model C photoelectric bomb fuze. Left view: cylindrical housing for fuze; center view: fuze and battery; 
right view: fuze mounted in adapter ready for screwing to tail of bomb. When installed on bomb, bars of fuze 
extend beyond bomb’s fin so that field of view of fuze is unimpaired. 


0.3 to 1.3 per cent over a 1,000-to-l ratio of light 
intensities. 

Standard hearing aid pentodes, Hytron HY-145, 
were used in the amplifier. Of several hearing aid 
tubes tried, this type most nearly met the desired 
characteristics for the photocell load. The pentodes 
were tested for microphonic stability and the best 
ones used in the input stage and the next best in the 
second stage. A Western Electric D-159778 thyra- 
tron was used as the trigger tube. 

The entire amplifier was embedded or “potted” 
in wax consisting of 16 parts ceresin and 1 part 


carnauba wax. The potting procedure insured main- 
tenance of a high input impedance over variable 
conditions of humidity and also prevented relative 
vibration of parts of the amplifier. Reliable per- 
formance of the fuzes in field tests was not obtained 
until the potting procedure was adopted. 1 - 104 
Power Supply. Electrical power for the vacuum 
tubes was supplied by dry cells. Three standard 
penlite cells were connected in parallel for the A 
battery, to give the required drain of about 300 
milliamperes at 1.5 volts. The B battery was built 
of 80 Type 132 cells built into 4 assemblies of 20 


38 


DESCRIPTION OF PHOTOELECTRIC FUZE TYPES 



cells each. It was tapped to yield voltages of 111, 90, 
21, 0, and —9. The B battery, A battery, and a 4- 
microfarad electrolytic capacitor formed the battery 
unit designated as Type X604. It was 2% in. in 
diameter and S 1 /} in. long. 

Arming. The arming system 1 * 3 consisted of a 
clockwork which operated a number of electrical 
contacts. When the bomb was released, the with- 
drawal of an arming wire set the clockwork in 
motion, and a switch was closed, which applied 
voltages to the filaments and plates of the vacuum 
tubes. Six seconds after release, corresponding to 
about 400 ft of vertical drop, a high resistor in 
series with the detonator was shorted, rendering the 
fuze active. Eighteen seconds after release, another 
switch closed, firing the detonator. The latter opera- 
tion occurred after about 5,000 ft of drop. Thus 
the “live” range of the fuze was between 400 and 
5,000 ft below the bomber. 

522 Model BR, or Mark 1, Fuze 3 104 

The Model BR fuze 96 - 97 followed essentially the 
same circuit design as was used in the Model C. 
Variations were in mechanical assembly and arming 
to allow use on rockets. A photograph of the BR 
model is shown in Figure 3. 

The arming system required the sustained acceler- 
ation of the rocket for its operation. The filament 
and plate supply voltages were connected at the 
start of setback and, about 0.1 second after the end 
of setback, the detonator was connected through a 
resistance-capacitance delay network. Self-destruc- 
tion [SD] was obtained with a clockwork, started 


by the setback switch. SD times could be set for 
either 15 or 30 seconds. 

All components in the fuze were required to with- 
stand an acceleration of 2,500(7. The pentodes 4)6 
used in the Model C were, with minor alterations, 
satisfactory in this respect. However, new thyra- 
trons and photocells were required. The Bell Tele- 
phone Laboratories [BTL] 1278 GY2 thyratron and 
the Radio Corporation of America [RCA] C-7052 
vacuum photocell were used. 

In this fuze, the look-forward angle was set at 25 
degrees, and the width of the field of view was 5 to 6 
degrees. 87 The fuze functioned on a decrease in light 
intensity of about 1.5 per cent (at the optimum rate 
of change). 

Most of the development work for the BR model 
was based on field tests with a special test rocket 
rather than with the British UP rocket. The latter 
rocket was not available in this country in any ap- 
preciable quantity; furthermore, its relatively long 
burning time (about 1 sec) and high dispersion 
made target tests difficult to carry out. For these 
reasons, Division 4 developed and procured a spe- 
cial rocket intended only for use in testing fuzes. 
This rocket is described in Section 9.1.1. The fuze 
designed especially for the test rocket was desig- 
nated Model AR, 3)104 and this fuze provided most of 
the engineering data for the Model BR. 

5 3 T-4 FUZE 84 

5,31 General Features 

The T-4 fuze for the M-8 rocket was a simplified 
and smaller version of the BR fuze. The major 


.S&A C 

^ w tun e ry Ttciiwiet-l Repoirt y^Yol. 3- Summary , photoelec- 
trie fuzes and miscellaneous projects, edited by A. V. 
Astin. Washington, D. C., 1946. 117 p. Contents. — 

1. Summary of work of Division 4. — 2. Proximity and 
time fuzes. — 3. Photoelectric fuze development; intro- 
duction ana summary. — 4* Basic principles and design 
of PE fuzes, by Alex Orden and R. F. Morrison. — 5. De- 
scription of photoelectric fuze types, by Charles Ra- 
vitsky, T. M. Marion, W. E. Armstrong and J. G. Reid, 
>/r. — 6. Laboratory methods for testing T-4 fuzes and 

Components, by P. J. Franklin 7. Field test methods 

for PE fuzes, by Alex Orden. — 8. Evaluation of PE 
fuzes, by Alex Orden — 9. Miscellaneous projects of 

( Owt ♦ 


JL 

Division 4> By Clarence B. Crane, L. M. Andrews, T. N. 
White and Robert D. Huntoon. 




and reports dated 


Division 4, by Clarence B. Crane, L. 
White and Robert D. Huntoon. 


M. Andrews, T. N. 


T-4 FUZE 


39 



Figure 3. Model BR photoelectric rocket fuze. Left, completely assembled fuze ready for installation on rocket. 
Next, from left to right, electronic assembly showing arming switch, cylindrical housing, battery, and rocket ogive 
which encloses battery. 


simplification was in the use of a thyrite 114 ’ 115 re- 
sistance element for the photocell load, followed by 
only one stage of amplification. A smaller, more 
compact battery 78 developed by the National Car- 
bon Company became available for the power sup- 
ply. The fuze and its major subassemblies are 
shown in Figure 2 of Chapter 3. 

The look-forward angle was set at 22.5 degrees 
and the width of the field of view at 4.5 degrees. 
Sensitivity was such that operation would occur on 
a 1.5 per cent change in light intensity. This corre- 
sponded approximately to the signal obtained in 
passing a medium bomber about 70 ft away. 

The nose, MC-380 ( ), was completely 

sealed 85 and contained the electrical components, 
consisting of the photocell-lens combination, the 
amplifier, and the thyratron. The parentheses con- 
tained the code letter, indicating the manufacturer; 


the letters A, B, C, and D indicating noses made by 
the Western Electric Company, the Westinghouse 
Electric and Manufacturing Company, the Rudolph 
Wurlitzer Corporation, and the Philco Corporation, 
respectively. The noses were interchangeable in the 
fuze. The front part of the nose formed the conical 
ogive for the rocket to which the fuze was assembled. 
The conical portion contained the pseudocylindrical 
Lucite lens. At the base of the conical portion was 
a shoulder 85 which contained slots for the wrench 
used to tighten the fuze in the rocket. The base of 
the nose contained two sets of threads. The smaller 
diameter threads were for assembly to the booster 
housing. The larger diameter threads were used for 
assembly to the rocket. Protruding from the base of 
the nose were the electric contact pins for connec- 
tion to the battery. The base of the MC-380 nose 
also contained a longitudinal red guide mark for 


CONFIDENTS 




40 


DESCRIPTION OF PHOTOELECTRIC FUZE TYPES 


proper alignment and assembly to the battery. Along 
the center of the guide mark was a groove used to 
secure proper alignment when the fuze was as- 
sembled in darkness. 

The battery, BA-75, 78 provided the electric power 
supply for operation of the fuze. It was encased in a 
black bakelite cylinder. The upper plate contained 
a 7-pin socket to receive the nose pins. The bottom 
plate contained a 6-pin socket to receive the switch 
pins. This plate had a notch to assist in securing 
proper assembly to the switch in darkness. 

The switch, SW-230, 77 contained the mechanical 
and electrical devices necessary to activate and arm 
the fuze, an electric detonator, and a powder train 
interrupter for safety during handling and launch- 
ing. Protruding from a fiber terminal disk at the 
top of the switch were the electrical contact pins for 
connecting to the battery. There was a metal cylin- 
drical case around the switch to protect the internal 
mechanism and explosive. At the bottom of the 
switch was a thick metal plate with a circular hole 
concentric with the switch. After the switch was 
armed, the tetryl pellet which detonated the booster 
charge was lined up with this hole. Arming occurred 
approximately 1 sec after launching, at which time 
the rocket would be about 500 to 600 ft 113 ahead 
of the launcher. 

The booster housing, M-381, 85 also acted as the 
encasing can for the battery and switch. It screwed 
onto the smaller threads of the fuze nose. In the 
bottom of the housing was a chamber containing a 
tetryl booster charge. There was a metal partition 
separating the booster from the switch. In the cen- 
ter of this partition was a circular hole which lined 
up with the hole in the switch plate. It was neces- 
sary to control the length of the booster housing 
in order to allow only a very small clearance 98 be- 
tween the tetryl booster and the bottom of the fuze 
well. 


The battery, switch, and housing were common 
to the T-4 and T-5 fuzes. c 

The table below lists the weights and dimen- 
sions of the components of the Fuze, Rocket, 
PD, T-4. 113 

Although the nose, the battery, and the switch 
were all tested when made, the possibility existed 
that they might no longer be in operating condition 
when the time came for the fuze to be used. The 
probability that the switch might have become de- 
fective without some visible damage having occurred 
to its case was extremely small, and the probability 
that the nose had become defective was only slightly 
larger. However, the battery had only a limited 
shelf life, so it was necessary to test it before as- 
sembling the fuze. Test Equipment IE-28 90,112 was 
therefore designed to test the components of the 
fuze under field conditions. These tests in the field 
were not so precise as the laboratory tests, but they 
permitted the rejection of fuze components which 
might have caused the fuze to malfunction. The new 
nature of electronic fuzes as ordnance items was a 
considerable factor in the decision to provide a field 
test set. Such test sets were not considered necessary 
for later fuzes (generator-powered radio fuzes). 

5 32 Mechanical Layout 

A picture of a cutaway model of the T-4 fuze 
is shown as Figure 4. It is completely assembled 
with the exception of the amplifier, which has not 
been potted, and the explosive booster, which has 
not been included. The four parts of the fuze, namely 
the MC-380 nose, the battery, the switch, and the 
booster housing, are clearly shown. The nose, 
MC-380, will be described in this section. 

The inner surface of the Lucite lens is coated with 
an optical black paint, 50 except for a narrow slit. 
The light incident on the lens from the look-forward 



Average 


Length 


Weight 

Diameter 

Assembled 

Unit 

(lb) 

(in.) 

(in.) Thread 

Nose MC-380 ( ) 

0.90 

3.187 ± 0.005 

3.3123 max 3.000-16-NS-2 

Battery BA-75 

0.60 

2.600 - 0.015 

2.312 - 0.020 

Switch SW-230 ( ) 

0.54 

2.600 - 0.015 

1.282 -0.010 

Booster housing M-381 

0.50 

2.875 + 0.010 

4.964 max 2.706-16-NS-2 

Assembled PD, T^4 

2.54 

3.187 ± 0.005 

7.567 max 

Depth inside rocket, M-8 




or M-9 fuze well 



5.250 min 

Length of fuze outside rocket 



2.3125 max 

° Reference is made to Division 

4, Volume 

1, for further details on 

the design of these components. 


CONFIDENTIAL 


T-4 FUZE 


41 


angle of 22.5 degrees is focused through the slit onto 
the photocell cathode. The outer surface of the lens 
is recessed beneath the surface of the ogive of the 
nose, formed by the nose cap and the amplifier 
housing, in order to protect the lens. A plastic photo- 
electric cell support is designed with very close 
tolerances so that the cathode will receive the light 
focused by the lens. The photoelectric cell support 
also insulates the photoelectric cell cathode from 
the housing, which acts as the electrical ground. 
The nose shield is fastened to the lens with machine 
screws which go into threaded holes. These holes 
do not extend into the field of view of the lens. A 
spring is compressed between the nose shield and 
the photocell, and thus keeps the photocell seated 
in its proper position. The photocell anode is insu- 
lated from the spring by a fiber insulating button. 
It is apparent from Figure 4, which shows the 
amplifier and the thyratron within the amplifier 
housing, that most of the space was wasted and had 
to be filled with the potting material; however, it 
was necessary to use the same housing as in the 
MC-382 nose for the T-5 radio proximity fuze, 
which required all that space. 

The nose cap was kept at ground potential in 
order to eliminate the possibility of the electron 
path within the photocell being affected by the 
large static charge which might otherwise build up 
on the nose in flight. It was therefore necessary 
that two wires pass through the field of view, one 
to ground the nose cap, and the other to keep the 
photocell anode at B-f- potential. It was required 84 
that these wires be bare within the field of view and 
be not larger than No. 28 B&S gauge. 

The slit was made on the inner surface of the 
Lucite lens in the MC-380(B), (C), and (D). In 
the MC-380(A), the slit was painted on the glass 
walls of the photocell. 108 If the sensitivity of the 
fuze was to be uniform in all directions, it was nec- 
essary that the edges of the slit be very clean and 
that the slit width be kept uniform throughout its 
length. Very uniform slits could be obtained by 
painting the Lucite, but it was found that the paint 
contained solvents which released strains in the 
Lucite lens, causing fine cracks to appear. The lens 
gradually deteriorated until it was no longer usable. 
Consequently, it was necessary to find a solvent for 
the paint pigment which would not cause this craz- 
ing of the Lucite. 61 ' 101 ’ 102 Although painting the slit 
on the photocell eliminated the crazing problem, it 


emphasized the problems involved in manufactur- 
ing the photocell. The glass wall was not always con- 
centric with the cathode and was not always circu- 
lar. The resultant variations in the position of the 



Figure 4. Cutaway of T-4 photoelectric fuze show- 
ing placement of components. 

slit with respect to the cathode produced a non- 
uniform sensitivity pattern for the lens-slit-photocell 
system. As the slit was closer to the cathode when 
it was painted on the photocell wall, a tilted cathode 


^CONFIDENTIAL 


42 


DESCRIPTION OF PHOTOELECTRIC FUZE TYPES 


caused a greater nonuniformity in the optical sen- 
sitivity pattern when this method was used than 
when the slit was painted on the lens. 

The amplifier was potted with the same ceresin- 
carnauba wax mixture used in the Model C fuze. 
Other mixtures with better antishrinkage properties 
were tried, 16 but none had as good electrical prop- 
erties as the wax. In a postproduction development, 
with a variation of T-4 designated as RPEB-2, 34 * 35 
it was found that a Glidden compound 27 > 28 had sat- 
isfactory electrical and mechanical properties. 

5 - 3 * 3 Electrical Layout 

The electric circuit used in the nose MC-380 is 
shown in Figure 5. 

In order to secure the proper amplifier character- 


arming. Leads to the detonator were brought 
through the battery, which occupied the space be- 
tween the amplifier and the switch. 

Noses MC-380 (A) , (B), (C), and (D) contained 
the electric self-destruction network, whereas noses 
MC-380 (D), (F), (G) , and (H) did not. 112 * 113 These 
latter noses could be assembled in fuzes which 
would destroy themselves if switches SW-200(B) 
or SW-230(B) were used. These switches contained 
a mechanical self-destruction contact set to operate 
6 seconds after firing. The switch shown in Figure 5 
is the SW-200. Switch SW-230 contained an elec- 
tric arming delay d which started to operate after 
mechanical arming had occurred. A resistor was 
mounted in the switch next to pin No. 6, so that the 
detonator firing condenser charged up through this 
resistor. 




Figure 5. Electric circuit of T^l fuze. Component values are shown in Table 1. Numbered terminals correspond to 
plugs and jacks on MC-380 nose, BA75 battery, and SW-200 switch. 


istics 14 - 19 when pentodes from different manufac- 
turers 23 were used, slightly different values of 
resistance and capacitance were necessary. These 
values are shown in Table l. 34 

The optical parts of the fuze were designed to be 
included within the fuze ogive. The input lead from 
the photocell to the amplifier had to be kept quite 
short in order to minimize possible leakage effects 
because of the high impedance of the network. It 
was therefore necessary that the amplifier be as 
close as possible to the photocell. The electric det- 
onator and the booster were placed at the bottom 
of the fuze to start the explosion. The detonator had 
to be part of the switch, as it was required that an 
interrupted powder train be used, and the switch 
contained the moving parts which could be used to 
move the detonator to line up the explosive train at 


5 - 3 - 4 Engineering Tolerances 

After a satisfactory fuze model had been devel- 
oped and successfully produced in pilot line produc- 
tion, 76 the transition to full-scale production 84 was 
made. The problems which arose then were due to 
the impossibility of making any two items identical. 
On the basis of the experience gained during pilot 
production, tentative specifications 77 - 86 , 88 , 89 , 91-95 f or 
the Fuze, Rocket, PD, T-4 were written. The toler- 
ances allowed in the various components and subas- 
semblies, and in the complete fuze, were necessarily 
compromises between fuze quality and fuze quan- 
tity. Wide tolerances would permit the production 
and acceptance of many more fuzes, but, obviously, 

d The action of this electric arming mechanism is explained 
in Division 4, Volume 1, Section 3.3. 


CONFIDENTIAL 


T-4 FUZE 


43 


Table 1 . Component values* 


Components 


MC-380 




RPEB-2 


T1 

936 

t 

t 

1P24 

t 

t 

t 

T2 

145ZT 

QF206 

SA781 

145ZT 

QF206 

SA781A 

GE QF206 

T3I 

ZG489 

GY2 

SA782B 

SA782B 

t 

t 

t 

T4 

NE23 

t 

t 

t 

t 

t 

t 

Cl 

0.0005 

t 

t 

0.005 

t 

t 

t 

C2 

0.02 

0.02 

0.02 

0.01 

0.003 

0.005 

0.005 

C3 

0.001 

t 

t 

t 

t 

t 

t 

C4 

0.002 

t 

t 

t 

t 

t 

t 

C5 

0.25 

t 

t 

t 

t 

t 

t 

C6 

1.7 

t 

t 

t 

t 

t 

t 

R1 

90 

t 

t 

10 

t 

t 

t 

R2 § 

none 

7.5 Q 

7.5 Q 

none 

5 Q 

5Q 

5Q 

R3 

4 

t 

t 

6.8 

10 

10 

10 

R4 

1 

t 

t 

2.2 

2 

2 

2 

R5 II 

none 

none 

2 Q 

2Q 

t 

t 

t 

R6 

2 

t 

t 

t 

t 

t 

t 

R7 

0.1 

t 

t 

t 

t 

t 

t 

R8 

35 

t 

t 

t 

t 

t 

t 

R9 

2 

t 

t 

t 

t 

t 

t 

RIO 

2 

t 

t 

t 

t 

t 

t 

VI If 


Varistor, class L, M, 

or N 


Varistor, class M, N, or high L 



* All capacitances in microfarads; all resistances in megohms, except where indicated, 
t Component value does not change, 
t Any thyratron may be used with any pentode. 

§ Pentode filament resistor. 

|| Thyratron filament resistor. 

H These classes are defined in terms of the varistor current for a potential drop of 110 volts; class L passes 50 to 90 microamperes, class M 
passes 90 to 150 microamperes, and class N passes 150 to 300 microamperes. 


fuze quality would suffer. The basic problem was 
that it was not known what the characteristics of a 
perfect fuze would be. Because of the exigencies of 
World War II, it was necessary to start production 
before these ideal characteristics could be deter- 
mined. The additional experience to be gained from 
quantity production and testing was required before 
it could be definitely determined what tolerances 
would be permissible for the various fuze parts. 
This section will deal with the subassemblies in the 
nose MC-380, and the separate components will be 
discussed in the section on components at the end 
of this chapter. 

Optical System. The variations in the optical sys- 
tem of the fuze arose from the variations in the 
lens, in the slit, and in the photocell, and in the 
mechanical accuracy with which these components 
were assembled. It was found that the angular 
width at which the light transmission of the system 
was less than 5 per cent of its maximum transmis- 
sion could easily be kept within 10 degrees when 
the slit was painted on the Lucite. However, a larger 
tolerance had to be allowed in order to include the 


model with the slit on the photocell. Some of the 
problems were that the glass wall was not a true 
cylinder, or that it did not form a right circular 
cylinder, or that the photocell cathode was not 
axially centered. The tolerances allowed in the 
photocell manufacture are discussed in Section 5.5. 

Studies 19 were made to determine the limits for the 
various components so that a fuze would work even 
though it contained several components which just 
met the specifications. The various subassemblies 
and the complete nose were also tested to make cer- 
tain that these variations would not affect fuze 
performance. Some tests were made of the uniform- 
ity of the optical system of the fuze by simulating 
the operating conditions. In general, the fuze saw a 
half-ring of sky of fairly uniform brightness and a 
half-ring of ground of roughly half the sky bright- 
ness. 54 In these tests, the nose was mounted axially 
inside a cylinder, half of which was white and half 
of which was black. The nose was then rotated, and 
the photocell current was measured. The ratio be- 
tween the minimum current and the maximum cur- 
rent formed a valid criterion of the uniformity of 


m 


CONFIDEN 



44 


DESCRIPTION OF PHOTOELECTRIC FUZE TYPES 


the optical system. In over half of the fuzes, the 
uniformity was 95 per cent or better, and, in over 90 
per cent, it was better than 85 per cent. 54 

Photocell Load Resistor. 38 ’ 41 As has been described 
in Chapter 4 of this volume, it was necessary to use 
a nonlinear element 1 * 3 in the fuze in order that the 
voltage signal at the thyratron grid be proportional 
to the percentage light signal input to the photocell, 
and independent of the steady background light 
level. It was shown that an element with a logarith- 
mic response would ideally meet these criteria. In 
the T-4 fuze, use was made of a nonlinear resistive 
element, known commercially as “varistor” 114 if 


order to determine what range of values of varistors 
should be used in conjunction with the photocells 
being used, taking account of manufacturing varia- 
tions in both the varistors and the photocells, graphi- 
cal calculations 42 were made in which all the pos- 
sible values of the two fuze components were cov- 
ered. The voltage output for a 1 per cent light signal 
was determined from these graphs for the different 
possible varistors. Figure 6 shows a set of these 
calculated curves for n — 5. The abscissa scales 
correspond to an average photocell, one only half as 
sensitive, and one twice as sensitive. The curve for 
the varistor with a resistance of 50 megohms at 1 


< 

z 

CD 

CO 



Figure 6. Voltage output across varistors for 1 per cent change in light level as a function of light level. Different 
curves represent different varistors labeled for voltage across varistor when it carries 1 microampere. Different 
abscissa scales correspond to photocell sensitivities of average, twice average, and half average values. 


made by the Western Electric Company, or as “thy- 
rite” 115 if made by the General Electric Company. 
The current-voltage relationship for this element 
obeys the equation I — kV n , so its response is not 
logarithmic; however, within the current limits set 
by the photocell used and the normal variations of 
daylight, 22 the response approximates a logarithmic 
curve adequately enough for use in the fuze. 

The nonlinear element, or varistor as it will be 
called hereafter, acted as a variable load resistor 
for the photocell. To specify the varistor, k and n 
in the equation I — kV n must be given. In the work 
on the photoelectric proximity fuze, the two charac- 
teristics 42 used to describe a varistor have been its 
exponent, n, and the ratio, V /I, in megohms, when 
a current of 1 microampere is flowing through it. In 


microampere was chosen as the “best” curve, as it 
gave the maximum voltage output over the entire 
useful range. Similar sets of curves were made for 
the other possible exponents, and the best responses 
were obtained for varistors 40/4, 50/5, 60/6, and 
70/7, where the numerator is the resistance in meg- 
ohms for a 1 -microampere current and the denomi- 
nator is the exponent n. Figure 7 shows the voltage 
output from the photocell-varistor network for a 1 
per cent light signal for each of these varistors. As 
the impedance of a varistor for a varying current 
is l/n times its resistance for a constant current, it 
is evident that the a-c impedance is 10 megohms 
at 1 microampere for each of the varistors chosen 
as having the most suitable characteristics. The 
normal background light level was 8 microamperes 


CONFIDENTIAL 

Hi ' 


T-4 FUZE 


45 



*.0« •• 0.25 0.5 1.0 2.5 5.0 ‘5.0 25.0 


LIGHT LEVEL IN TERMS OF PHOTOCELL CURRENT iJU A) 

Figure 7. Voltage output across four different varistors as function of light level. Ordinate and abscissa scales are 
as in Figure 6. See text for description of varistors. 


in the standard lens-photocell combination, so cal- 
culations were made 42 to determine if a reference 
current level somewhere between 8 microamperes 
and 1 microampere, say at 4 microamperes, might 
be better than the 1 -microampere level for determin- 
ing the equality of varistor impedances for alternat- 
ing current. It was found that the spread of output 
voltages from the photocell-varistor combination 
for a 1 per cent light signal, using varistors whose 
a-c impedances were equal to 4 microamperes, was 
greater than when the impedances were equal at 1 
microampere. 

As a result of these investigations, it was decided 
that a satisfactory range in varistor values existed 
which would provide adequate output voltages over 
the entire range in light levels even after allowing 


for a wide variation in photocell sensitivities. The 
voltage-current curves for varistors 40/4, 50/5, 60/6, 
and 70/7 are shown in Figure 8. Any varistors whose 
voltage-current curves were within these limits be- 
tween 0.4 microampere and 24 microamperes were 
acceptable. These current values covered the range 
of photoelectric currents produced in any acceptable 
lens-photocell combination 76)84 by the background 
light level during daylight. 

At low light levels, the peak of the frequency 
response curve of the amplifier is shifted toward 
lower frequencies as the light level is decreased. 29 
This effect arises because of the capacitance asso- 
ciated with the nonlinear resistance. Capacitances 
of the General Electric thyrites have been measured 
and found to vary from 25 to 55 micromicrofarads, 



MICROAMPERES 

Figure 8. Voltage-current characteristics of four varistors. See text for method of designating varistors. 



46 


DESCRIPTION OF PHOTOELECTRIC FUZE TYPES 


with an average value of about 30 micromicrofarads. 
At 120 c, the impedance of a 30-micromicrofarad 
capacitance is 44 megohms. The effect of this shunt is 
important only at low light levels, as the a-c imped- 
ance of the nonlinear resistance is small in compari- 
son to 44 megohms except for small photocurrents. As 
the current decreases, the resistance of the varistor in- 
creases exponentially, while its capacitance remains 
virtually constant. Thus there is a decrease in the 
amplification of the unit as the light level is de- 
creased for a signal at any frequency. Overall sen- 


is included in Figure 5, which shows the electric 
circuit diagram for the entire fuze. The frequency 
response curve for the amplifier, 14 indicating the 
relative amplitude of the output signal as a function 
of frequency, was shown in Figure 15 of Chapter 4. 
This curve was the average curve for two amplifiers 
built with accurately chosen components. The nomi- 
nal supply voltages of 1.5 volts for the A supply 
and 138 volts for the B supply were used. In opera- 
tion, the fuze battery voltages were usually less 
than these nominal values, and measurements were 



LIGHT LEVEL IN MICROAMPERES 

Figure 9. Threshold (inverse sensitivity) of T-4 fuze as function of light level. 


sitivity involves the changing effects of both the 
amplifier and the nonlinear input resistor and is 
obtained most readily by the method described in 
Section 6.2.3 for threshold measurement (inverse of 
sensitivity) . Figure 9 gives the threshold in terms of 
per cent light signal for an average unit for a 60-c 
light signal, as a function of the background light 
level. 68 The thresholds increase slowly as the light 
level is decreased from 3 times the normal back- 
ground level to one-quarter of the normal light level. 
Below this level, the thresholds increase quite rap- 
idly as the light level is decreased. 

Effect of Supply Voltage Variations . The basic 
design of the amplifier was discussed in Chapter 2 
of this volume. The circuit diagram of the amplifier 


made to determine how low the actual voltages 
could be without unduly affecting proper fuze func- 
tions. As the voltage decreased from 1.50 volts, 
there was no reduction in gain until the filament 
potential was reduced to 1.15 volts. 4 Thereafter, the 
gain fell rapidly. At 1.00 volt, the average gain 
was 92 per cent of maximum, and, at 0.90 volt, the 
average gain was only 78 per cent of maximum. 

Sensitivity as a Function of Light Level. Although 
the ideal photoelectric proximity fuze is independent 
of the light level, this goal was not possible with 
the simplified circuit used in the T-4. It was de- 
cided that the small variation in fuze sensitivity as 
a function of light level was less important than 
simplicity in construction. At the normal light level 


CONFIDENTIAL 


EXPERIMENTAL MODELS 


47 


(see Chapter 4) , a light signal of less than 0.8 per 
cent would fire the fuze, whereas, at a light level 
only one-eighth as bright, a 2.2 per cent light signal 
is necessary. 

Input Impedance. The impedance 29 of each of the 
components 43 used in the input circuit was neces- 
sarily quite high because of the very high impedance 
of the vacuum photocell used. The effect of a light 
signal incident on the photocell was to cause a cur- 
rent signal to flow through the impedance network. 
The magnitude of the current pulse was practically 
independent of the impedance values, so the larger 
the input impedance, Z, of the pentode 5 was, the 
larger the voltage signal at the pentode grid would 
be. In the average fuze, the voltage signal required 
to cause the amplifier to fire the thyratron was 
about 0.1 volt peak. The amplifier gain at the signal 
frequency was about 40, and the thyratron holding 
bias was between 3 and 4 volts. The frequency at 
which the pentode network had its maximum ampli- 
fication was about 130 c. At this frequency, the im- 
pedance of the 0.0005-microfarad condenser was 
about 2.5 megohms. The input impedance of a good 
pentode, as used in the amplifier, was about 20 
megohms. 53 One of the major problems which arose 
in manufacturing the nose, MC-380, was the de- 
crease in the input impedance 29 of the pentodes 
with age. Gas would be evolved in the tube in stor- 
age because of imperfect evacuation of the gas dur- 
ing the manufacture of the tube, and the input 
impedance of the tube would decrease tremendously. 5 
In some tubes there was an impedance decrease by 
a factor of about 15, which caused a decrease in 
sensitivity of the fuze by a factor of only 2 at normal 
light levels, but at low light levels by a factor 
of 5. 29 The gas in these tubes would be absorbed by 
the getter if the tube were operated for a few min- 
utes before using the fuze, but provision for such 
operation would be difficult in Service use. In the 
condenser-powered fuze, 8 * 9 described in Section 5.4, 
a method to overcome this difficulty is discussed. 
Large plate and screen resistors were used, so that 
the electron current in the tube, which might cause 
ionization of any gas present, was decreased. Much 
more important, however, was the result that, with 
the large series resistors, the electrode potentials 
were below the minimum ionization potential for any 
gas that might be in the tube, so only minute quan- 
tities of ionized gas were possible. 

Another method of reducing the input impedance 


problem was the use of more sensitive photocells and 
lower impedance varistors. Some of these changes 
were incorporated in the post-production model of 
the RPEB-2. 34 ' 35 

5 4 EXPERIMENTAL MODELS 

5,41 Generator-Powered Rocket 

Fuzes [RPEG] 

In order to eliminate the deficiencies of the bat- 
tery power supply of the T-4 fuze, developments 
were initiated to replace the battery in the fuze by 
a generator power supply. 17 ' 198 Designs were adapted 
to the exterior dimensions of the T-4 fuze in order 
that the new fuze, designated RPEG (Rocket, PE, 
Generator) , could replace it. 

The power supply for the photoelectric-type fuze 
had to perform under the same general conditions 
as that for the radio-type fuze. e The same qualities 
of long storage life, mechanical and electrical sta- 
bility, independence of ambient conditions during 
the service period or storage, ruggedness, small size, 
and simplicity of production were desired. Require- 
ments differed only in that the PE electronic as- 
sembly had a significantly smaller electric power 
demand than the radio-type unit. The potentials 
involved were the same in the two cases, 130 to 150 
volts d-c for plate supply, 1.3 to 1.5 volts a-c for 
filament supply, and —6.0 to —7.5 volts d-c for 
the C bias. However, the lighter current drain of the 
photoelectric unit gave an aggregate power require- 
ment of less than 1 watt in service as compared with 
approximately 5 watts for the radio unit. 

This smaller power requirement rendered the 
delayed service and low-temperature deficiencies of 
dry batteries less serious for the photoelectric unit 
than for the radio unit and also permitted consider- 
ation of power supply systems which were not prac- 
tical for the radio unit (cf condenser-powered fuze, 
Section 5.4.3) . However, the ultimate solution of the 
power supply problem appeared to lie in the use of 
a rotary permanent-magnet alternator, wind-driven 
by the flight of the projectile/ Experimental devel- 
opment was done on generator-powered photoelectric 
fuze RPEG for use with the M-8 rocket 17 and 
generator-powered photoelectric fuze BPEG for use 
on bombs 108 which accepted the M-103 point-det- 
onating fuze. 

e These requirements are discussed in detail in Division 4, 
Volume 1. Section 3.4. 

f Cf Division 4, Volume 1, Section 3.4. 


CONFIDENTIAL 


48 


DESCRIPTION OF PHOTOELECTRIC FUZE TYPES 


In both cases, the necessity of mounting the 
photoelectric cell and its optical system centrally at 
the nose of the fuze complicated the overall design. 
This precluded the use of a nose-mounted propeller 
with a central drive shaft to the generator, or of a 
central air duct to a turbine mounted at the base 
of the fuze, the designs which were favored in the 
generator-powered radio units (see Figures 2 and 3, 
Chapter 1). In consequence, both RPEG and BPEG 
made use of peripherally located air scoops and 
ducts, with rim-driven turbogenerator assemblies 
mounted at the base of the fuze. 

The general design followed in the development of 
RPEG is shown in the schematic section drawing 
of Figure 10. The nucleus of the unit was the cen- 
trally located metal can which housed the electronic 
assembly and the power supply. The metal nose cap 
and the annular Lucite lens completed its foresec- 
tion. The rotor of the turbogenerator was carried on 
a stationary stub shaft projecting from the rear of 
the assembly. 



Figure 10. Photoelectric generator-powered rocket 
fuze, RPEG. Axial section is shown schematically. 
Path of air through ducts and driver turbine is indi- 
cated by arrows. 

A tubular metal cowl, flared toward the nose end, 
was mounted coaxially on the electronic power sup- 
ply container, spaced out from it by three %-in. 
bosses to provide an air intake duct. These parts are 
shown in Figure 11. A larger tubular metal piece 
was mounted coaxially and Ys in. out from the intake 
cowl to provide a counterflow exhaust duct. This is 
shown in Figure 10, where the arrows indicate the 
airflow through the duct system and the turbine 
blades. The outer tube also served as a mounting 
for the arming and detonator assembly. The RPEG, 
mounted in a rocket, is shown in Figure 3, Chapter 3. 

The generator and electronic assembly of an ex- 
perimental model are shown in Figure 12. The elec- 


tronic assembly was essentially that of the MC-380, 
rearranged and reduced in size to the required 2 in. 
OD. The generator consisted of A and B windings 
distributed on three bobbins, each mounted on a 
U-shaped lamination stack as shown. The turborotor 



Figure 11. Photoelectric generator-powered rocket 
fuze, RPEG. At left, experimental model with impro- 
vised housing for arming switch SW-200 attached at 
rear. At center, electronic and power supply assembly. 

At right, cowling member for directing air to and 
from turbine. 

was a bakelite disk 2% in. OD and % 6 in. thick. 
The turbine blades, 26 in number, were molded on 
its periphery. Three bars of Alnico III magnet steel, 
Y± in. square in cross section and 1 in. long, were 
molded as inserts in the turborotor. After molding, 
these were magnetized to activate the magnetic cir- 
cuit of the generator. 

The circuit for regulating the output voltages of 
the generator against variations due to change in its 
rotational speed, the B-supply rectifier, and the fil- 
ter were of the same type as were used in the radio- 
type fuzes.* 

The RPEG project was included in the general 
termination of work on PE fuzes. The photographs 
shown here represent the status of model production 
at the termination date. The model described (Fig- 
ure 12) had passed a number of laboratory tests but 
had not been subjected to field tests on rockets. 

A number of projected improvements had not yet 
reached model production at the termination date. 
These included: 

1. A single-coil generator utilizing a magnetic 
stator stamped as part of the steel can which housed 
the electronic assembly. The magnetic rotor was a 

g These are described in detail in Division 4, Volume 1, 
Section 3.4. 


EXPERIMENTAL MODELS 


49 


disk of Alnico II, 1 in. OD by % in. thick, molded 
on the face of the turborotor and mounted reentrant 
into the stator as shown in Figure 10. 

2. An electrically redesigned amplifier having 
higher peak gain and a much narrower passband, 
with upper cutoff frequency below the rotational fre- 
quency of the generator during service. 11 


predetermined number of turns. If setback force 
were removed prior to this locking, the clutch nut 
returned to the unarmed position. 

Although no working models were produced for 
testing, a workable basic design for RPEG ap- 
peared to have been completed at project termina- 
tion. 



Figure 12. Photoelectric generator-powered rocket fuze, RPEG. At left, electronic and power supply assembly. At 
right, unit disassembled to show electronic and generator stator subassembly and turborotor. (Note detonator leads 
which are fed through hollow shaft.) 


3. An arming system actuated by the combina- 
tion of air travel and setback. This was to operate 
through a clutch from the back face of the turbo- 
rotor. The clutch used a spring-biased split nut on 
a ratchet thread and engaged under the action of 
setback forces. It was locked into engagement by a 

h Cf amplifier design for generator-powered radio proximity 
fuzes, Division 4, Volume 1, Chapter 3. 


5 ' 4 ' 2 Generator-Powered Bomb 

Fuzes [BPEG] 

The generator-powered PE bomb fuze [BPEG] 108 
was developed for use on bombs which mounted the 
M-103 point-detonating fuze. This unit is shown in 
Figure 4, Chapter 3. The small-diameter cylindrical 
section seated into the bomb fuze well, secured by 



50 


DESCRIPTION OF PHOTOELECTRIC FUZE TYPES 


a 2xl2-in. thread at its upper end. The larger section 
of the fuze, S 1 /^ in. OD by 4% in. long, projected 
from the nose of the bomb. Figure 13 shows the unit 
disassembled into its principal subassemblies. The 
electronic assembly, including photocell and lens, 
was mounted in the nose section of the unit. Imme- 
diately behind were the generator and power supply. 



Figure 13. Photoelectric generator-powered bomb 
fuze, BPEG, disassembled into principal subassem- 
blies. At top, electronic unit, with photocell and lens. 

At left, power supply, arming and detonator assembly. 

At center, unit housing. At right, air director cowl. 
Below, unit base housing and, at right, insulating 
washer. (Photograph by Bell Telephone Laboratories.) 

Arming, detonator, and booster elements were 
housed in the rear part of the fuze well section. Since 
the turbine was not mounted within the fuze well, 
no counterflow exhaust duct was required. Intake 
and exhaust ports for the turbine cavity can be seen 
in the cast brass housing which is centrally located 
in Figure 13. The tubular brass cowl (seen at right, 
center, in Figure 13) was assembled around the cast 
housing to provide a peripheral intake scoop and 
exhaust apron for the ports. 

The BPEG power supply, in respect to circuit de- 
sign, components, and operating characteristics, was 


essentially identical with that of the P-4 radio fuze 
(Bell Telephone Laboratories designation). 1 

As shown in Chapter 8, a small sample of BPEG 
fuzes gave good performance in field tests on 
bombs. 

5 * 43 Condenser-Powered Fuzes 

It was found that because the PE fuze operated 
on a very low B and C current drain, it was feasible 
to employ for the B and C and thyratron plate sup- 
plies a pair of capacitors which were charged just 
before the unit was fired. 8 ' 9 The condensers are not 
subject to the limitations of temperature and shelf 
life as are batteries and thus are simpler, cheaper, 
and easier to procure. 

Besides the substitution of the charged condensers 
for the batteries, these units incorporated other ad- 
vantages not necessarily characteristic of the con- 
denser-driven circuit alone. The circuit diagram is 
shown in Figure 14. The high impedance of the plate 
and screen load resistors caused the pentode to oper- 
ate with such low plate and screen voltages that the 
effect of the residual gas in the pentodes, 5 which led 
to some difficulties in the T-4, was eliminated. The 
magnitude of the thyratron grid bias was propor- 
tional to the current drain through the photocell and 
the pentode. As the charge was drained from the 
condenser, the diminution of the current through 
the pentode reduced the thyratron bias, making the 
unit progressively more sensitive after firing. This 
was considered an advantage because a unit which 
is fired at the more distant targets is likely to re- 
quire greater sensitivity for proper functioning. Ten 
or twelve seconds after firing, the bias would become 
so low that the thyratron fired in the absence of sig- 
nal, and any need for an auxiliary circuit for self- 
destruction was eliminated. The unit was far supe- 
rior to the T-4 in its threshold flatness characteris- 
tic; that is, its overall sensitivity did not vary as 
much with light level. At lower light levels, the lower 
photocurrent supplied lower thyratron holding bias, 
and this tended to compensate for the loss in am- 
plifier sensitivity at the low light levels. 

The condenser-powered fuzes which were built 
used the same housings as the T-4 fuze. As shown in 
Chapter 8, field tests 12 of the modified unit were 
very satisfactory. 

Reserve Batteries , 64 For use with the condenser- 


iThis is described in Division 4, Volume 1, Section 3.4 

CONFIDENTIAL 


EXPERIMENTAL MODELS 


51 


SQUIB 



41.5V 

< UvM — If—' 

210 



Figure 14. Circuit diagram of condenser-powered modification of T-4 fuze. Resistance values (unless followed by 
co) are in megohms; capacitance values are microfarads. 


powered fuze, the National Carbon Company devel- 
oped a reserve A battery. Only 6 of the condenser 
fuzes used in the field tests were equipped with these 
reserve A batteries, and all 6 functioned properly. 
This indicated that full voltage was developed be- 
fore arming and that no transients occurred of suffi- 
cient size to fire the fuze prematurely. This reserve 
battery consisted of a zinc outer electrode, cylindri- 
cal in form, a similarly shaped, carbonized steel 
interelectrode, a glass ampoule containing the elec- 
trolyte (in this case, chromic acid and sulphuric 
acid) , and a lead weight supported by a shear wire 
for breaking the capsule during setback. 

The advantage of the reserve battery 13 > 72 over a 
regular A battery is its indefinitely long shelf life. 
When a condenser-powered fuze employs it for an 
A supply, the entire unit has an indefinitely long 
shelf life. Its disadvantage is the possibility that the 
ampoule in the battery will be broken by rough 
handling. 

Heater Cathode Tubes. As it is characteristic of 
heater-type cathodes to continue to emit for some 
time after the heater voltage is turned off, it is pos- 
sible to construct condenser-driven units employing 
heater cathode tubes 15 that would contain no A 
supply whatever. The cathodes could be heated by 
an external power source before firing and during 
flight would stay hot enough to maintain the tube 


transconductance. Pentodes of this type that were 
built for PE fuze operation were found to retain 
their mutual conductance for longer than 10 sec 
after the heater voltage was turned off, 15 and this 
would satisfy most antiaircraft fuze requirements. 
Since these tubes required heating in excess of 5 
seconds for proper operation, it would be necessary 
to heat the cathode continuously during all times of 
possible emergency use. This would necessitate a 
long life on the part of the tubes and operation at 
temperatures low enough not to damage the re- 
mainder of the fuze. 

To realize the full advantages of the heater cath- 
ode pentodes, the development of heater cathode 
thyratrons is indicated. Also it would avoid compli- 
cations in the external power supply mechanism if 
both the pentode and thyratron cathodes could be 
heated by the same power source which supplies the 
voltage for the condensers. 

Photothyratrons . 56 For the purpose of eliminating 
the need of an A voltage supply, a thyratron was 
developed which had a photosensitive surface in- 
stead of a filament as a source of electrons. This 
thyratron was essentially a gas photocell with a grid 
mounted between the anode and cathode. The devel- 
opment of these tubes did not proceed very far, but 
some of them seemed quite promising. The critical 
grid voltage was a function of the plate voltage, the 


CONFIDENTIAL 


52 


DESCRIPTION OF PHOTOELECTRIC FUZE TYPES 


grid leak resistance, and the light level on the cath- 
ode, but in some tubes it had very little dependence 
on light level. Emission from the grid was a disad- 
vantage in some tubes. 

The use of these thyratrons in zero stage fuzes 51 > 52 
(no amplifier) or fuzes which employ amplifier tubes 
with photoemissive surfaces as cathodes would 
eliminate the need for an A supply, either internal 
or external. 

5 ' 4 ' 4 Non-Sunfiring and 

Non-Sunblinding Fuzes 

The normal T-4 fuze would fire prematurely if, 
after arming, the field of view were made to include 
the sun or to view the sky at a small sun angle 24 
(see Chapter 8). The sun angle was defined as the 
angular difference between the direction from the 
fuze, of the sun, and of the center of the field of view 
nearest the sun. This premature firing was believed 
due to the rapid varying of the sun angle by the 
yawing of the projectile in flight, and laboratory 
experiments with units on yaw machines supported 
this belief. 

Even if the sun in the field of view would not fire 
the fuze, it would cause such a large current in the 
photocell that any change due to a target that did 
not obscure the sun would be too small by compari- 
son to trigger the fuze. This phenomenon is called 
sunblinding. 

Photographic records were made of the voltage 
transients set up in the fuze by yawing the units 
through the sun on a yaw machine. They revealed 
that the general form of the signal across the load 
resistor as a function of sun angle, dv/dd, was as 
shown in Figure 15. 

The slow change of voltage with respect to angle 
at sun angles greater than 3 degrees was caused by 
the bright region of the sky near the sun. The steep 
sides at about 3 or 4 degrees were due to the sun’s 
emergence into or disappearance from the field of 
view. The top was flat, for the photocell was too 
conductive to impede the flow of current when the 
sun was in the field of view. The small spike at the 
top was caused by an unexplained discontinuity in 
the voltage-current characteristic of the photo- 
cell. 

The T-4 fuze would fire on the sudden application 
of an obscuration signal if the time rate of voltage 
change across the photocell load resistance, dv/dt, 


exceeded the critical value for a sufficient time inter- 
val. 31 For signals due to the sun, 

dv dv dO 

dt dO dt' 

At sun angles greater than 3 degrees, this quan- 
tity may be of firing magnitude provided dO/dt is 
large. The magnitude of dO/dt depends, of course, 



Figure 15. Voltage signal developed across photocell 
load resistor as function of sun angle (angle between 
sun and center of field of view). 


on the angular velocity of the projectile. At sun 
angles at which the sun enters and leaves the field 
of view, dv/dO is so large that dO/dt can hardly be 
made so small that dv/dt can be reduced below the 
critical value. 

The characteristics of the photocell load resistor 
are such that if i is the photocurrent and k is a 
constant, then dv = k{di/idt) and firing may be 
said to occur when k/i{di/dO) ( dO/dt ) exceeds a 
critical value. 

Double Photocell Circuits. The only known PE 
circuit which gave promise of preventing sunblind- 
ing as well as sunfiring was one that employed two 
photocells 44 - 48 > 49 and two fields of view 20 so sepa- 
rated that the sun could not be in both at the same 
time. This would be quite an important factor in 
plane-to-plane firing for, as the trajectory does not 
change much during flight, there is a high probabil- 
ity that a unit which required protection against 
sunfiring before reaching the target would also re- 
quire protection against sunblinding upon reaching 
it. 

Two general arrangements of input circuits em- 


CONFIDENTIAL 


EXPERIMENTAL MODELS 


53 


ploying two photocells were considered. One is shown 
in Figure 16. 

As either photocell receives a signal on passing a 
target, the voltage signal developed across its varis- 
tor is reduced by a factor of approximately two by 
the other photocell-varistor combination. As the 
sunlight is received by either cell and renders its 
impedance very low, the impedance of the series 



Figure 16. Circuit for anti-sunblinding photoelectric 
fuze using two photocells and two lenses. Elements in 
rectangles are nonlinear resistances. 


varistor is maintained high by the current-limiting 
action of the series resistor. It appeared that sun- 
firing could be prevented by the series resistor. 31 If 
it could be made to limit the current through the 
photocell to values for which the quantity di/dO is 
low, the sun signals would not contain high-fre- 
quency components sufficient to operate the ampli- 
fier. 

In order that the fuze be sensitive to target sig- 
nals and not sunfiring, it is necessary that the 
series resistor be low enough to permit the cell to 
control the current when the sun angle is large 
(di/d6 small) and yet high enough to limit the cur- 
rent when the sun angle is small ( dv/dd large). As 
the illumination of the sky varies quite widely from 
time to time, it seems impossible that a single value 
of resistance would meet both of these require- 
ments. 37 The photocurrent produced as a cell views 
any portion of a bright sky may be greater than 
that produced at another time as the cell views a 
dark sky and the sun is actually entering the field 
of view. 


The second arrangement of the two photocells is 
shown in Figure 17. 

If the photoemission in each cell is about the 
same under normal sky illumination, the unit can- 
not be sunblinded. If either cell receives the direct 
sunlight, it is effectively short-circuited, and the 
behavior of the unit will then be almost exactly the 
same as that of the normal T-4 fuze with the other 
cell controlling the current. If the current through 
a photocell is less than its photoemission will permit, 
its electrical impedance is extremely low because of 
the nature of its voltage-current characteristic. 

If, because of change in the fuze’s trajectory, the 
sunlight is received by the cell which is normally 
the more conductive, its impedance, already ex- 
tremely low, is merely rendered somewhat lower, 
and no significant change in the current occurs. 

As the sunlight is received by the cell which is 
normally less conductive, the current through that 
cell increases to the amount that the other cell is 
capable of passing under its normal illumination. A 
voltage change is thereby produced across the load 
resistor. Experiments have shown that, since the 
photoemission in each cell is normally very nearly 


B* 



Figure 17. Alternate circuit for anti-sunblinding 
photoelectric fuze. 

the same and the fields of view are widely separated, 
the voltage change will not fire the unit as it is 
yawed through the sun. But, if one cell has a photo- 
emission that is normally only 90 per cent as great 
as the other, or less, and is carried in and out of the 
sunlight at high angular velocities, sunfiring will 
generally occur. This is because the current change 
with angle in this case is quite large and is sharply 
discontinuous as the limiting action occurs. The 
general form of the yaw signal (voltage versus time) 


CONFIDENTIAL 


54 


DESCRIPTION OF PHOTOELECTRIC FUZE TYPES 


is then that of a sine wave with the peaks cut off 
sharply on one side. An amplifier with the passband 
of the T-4 fuze has a high gain for a signal of this 
form. Its large-amplitude low-frequency compo- 
nents may be adequately attenuated, but its sharp 
discontinuities produce voltage transients in the 
amplifier which are as fast as those expected to be 
received from the target and to trigger the fuze. 

Reduction of the sharpness of such discontinuities 
in the yaw signals may be accomplished by several 
methods, all of which serve to decrease the quan- 
tity di/idO or the sharpness with which it changes. 
The photocells may be selected in pairs to have 
nearly equal photoemission. The fields of view may 
be separated quite widely and may be made wide 
for small percentage widths. High resistances, either 
linear or nonlinear, may be placed across the less 
conductive cell. All of these methods were found to 
have some degree of effectiveness, but the problems 
had not been completely resolved before work was 
terminated. 

One modification of this circuit which was found 
to give good protection under most conditions of 
yaw was that of replacing one of the photocells with 
a parallel combination of a much less conductive 
photocell and a 3- to 5-megohm resistor. Normally, 
the other photocell controls the current, but as it 
receives the sun, its current is limited by the parallel 
combination without becoming very large or sharply 
discontinuous at any time. Protection against sun- 
firing is lost only if the sky illumination is so great 
that the single cell does not normally control the 
current or so low that the current-limiting action of 
the parallel combination is inadequate. Under most 
levels of illumination, the protection seemed ade- 
quate under most conditions of yaw. 

It seems likely that the ideal type of cell to use in 
series arrangement for prevention of sunfiring would 
be one whose dynamic impedance is proportional to 
the voltage across it and inversely proportional to 
the illumination upon it. Then, as the less conductive 
cell was carried in and out of the direct sunlight, the 
manner in which the other cell would assume and 
release control of the photocurrent would be such as 
to reduce the sharpness of the discontinuities to a 
minimum. A possible approximation to this ideal 
cell is one which has a large space charge effect 
throughout the operating range. No experiments 
were done with a cell of this sort. 

The type of signals received from targets may be 


modified so that discrimination in their favor can 
be more easily accomplished in the circuit. Restric- 
tion to small widths of the field of view for large 
percentage widths would make sharper the signals 
received from the target. This does not necessarily 
conflict with the previous suggestion of making the 
field of view wide for small percentage widths. 

Circuit with Modified Input. One simple modifi- 
cation of the T-4 input circuit was tested and found 
to be proof against sunfiring. 37 It had no sensitivity 
at light levels greater than 1.5 lumens, so that its 
use would have been restricted to low light level 
applications, such as ground approach firing. The 
circuit modification 31 > 37 is shown in Figure 18. It 



Figure 18. Modification of input circuit of T-4 fuze 
to prevent sunfiring. Elements in rectangles are non- 
linear resistors. 


comprised the standard MC-380 circuit components 
with the addition of a linear resistor and a nonlinear 
resistor, and having the input coupling condenser 
reduced from 0.005 to 0.002 microfarad. The linear 
resistor, R 0 , in series with the photocell, must be ad- 
justed to values between 0.5 megohm to 2.0 meg- 
ohms, depending on the photocell sensitivity. 

The three main factors that contributed to mak- 
ing this modification proof against sunfiring were: 

1. The negative mismatch of the load resistance 
to the cell reduced the variation of voltage with 
photocell current across the load resistance at high 
light levels. 

2. The grid-to-ground impedance was rapidly re- 
duced as the photocell current rose. 

3. As the voltage across R B was increased, volt- 
age was applied in increasingly larger proportions 
to the grid of the amplifier due to the action of the 
nonlinear coupling resistor. The operating point of 
the tube was shifted to regions of extremely low 
gain by the high positive bias. 


CONFIDENTIAL 


i 


PHOTOCELLS 


55 


Twenty-five of the modified fuzes were tested for 
sunfiring properties on the yaw machine and found 
satisfactory. Equally good results were found in field 
tests (see Chapter 8) . 

5-4-5 Zero Stage Fuzes 

In the interest of simplicity, attempts were made 
to develop a satisfactory zero stage fuze, that is, a 
circuit employing no stage of amplification. 51 * 52 The 
magnitude of the photocurrents employed in the T-4 
fuze was such that, at all light levels except the very 
lowest, an obscuration signal of 10 per cent was 
capable of firing an amplifier, provided the dynamic 
load impedance was sufficiently high. This imped- 
ance consisted of the parallel combination of the 
thyratron grid leak resistor and the photocell load 
resistor. 

A number of zero stage units were built in which 
a 20-megohm resistor was employed as a photocell 
load resistance, a 20-megohm thyratron grid leak 
resistor was used, and a condenser charged to 315 
volts was employed as the B supply. A high B volt- 
age was necessary because of the high voltage drop 
developed across the 20-megohm load resistor at the 
higher photocurrents. Dispersion of available rock- 
ets prevented proper field evaluation of this circuit. 
This is, of course, significant since the fuzes were 
intended for use on rockets, and, if the complete 
round were not brought close enough to the target 
for function, the weapon would be of no value. 

In other experimental units, a second photocell 
which viewed the sky at a slightly different angle 
was used as a load impedance. When the photo- 
emission from each cell was approximately the same, 
each cell served as a high dynamic impedance load 
on the other. Under these conditions, the unit was 
more sensitive than the single-cell zero stage unit, 
the sensitivity was fairly independent of light level, 
and the unit, unlike the T-4, was as capable of 
responding to a bright target as to a dark one. Its 
chief difficulty was that of making the photoemis- 
sions of the two cells near enough to the same value. 
Because of the nature of the photocell voltage- 
current characteristic, the range of photocurrents 
that a photocell can pass with a given photoemission, 
while maintaining a high dynamic impedance, is 
quite restricted. 

If, instead of vacuum photocells, gas-filled photo- 
cells are used, the problem of making the photo- 


emission in each cell nearly the same is no longer 
very serious. The sensitivity for the balanced condi- 
tion is less than that obtained with vacuum cells, 
but experiments indicated that such units with 
thresholds of 1 to 3 per cent were feasible. 

5-4,6 Active-Type PE Fuzes 

Preliminary calculations and experiments were 
made on the possibility of operating an active-type 
PE fuze. 39 * 40 They indicated that a very sensitive 
PE fuze should operate at night by the light reflected 
by a target at distances up to 50 ft if the target is 
illuminated by a searchlight beam or a light of 
about 100 candlepower carried by the missile. In 
either case, the fuze would have to operate on ex- 
tremely weak light signals. 

The most promising type of amplification for a 
fuze of this type seemed to be that of the electron 
photomultiplier tube. It would respond to extremely 
weak light signals and would not be subject to as 
many sources of noise as is a conventional amplifier. 
No models of active-type fuzes were built. 

55 PHOTOCELLS 

5-5-1 General 

Since the photoelectric cell is the nucleus of a PE 
fuze, considerable effort was spent in developing a 
satisfactory cell for fuze use. High sensitivity, rug- 
gedness, and resistance to microphonics were prime 
requirements. A secondary requirement was the 
color characteristic. Peak sensitivity in the blue was 
desired in order to reduce contrast between the sky 
and clouds. 1 ’ 3 

After numerous interim models, a “cartridge” 
type of high-vacuum photocell was designed (see 
Figure 19) . It consists of a cylindrical glass tube to 
which are sealed the anode and cathode “headers.” 
This photocell has the following advantages: (1) it 
is simpler to make; (2) it eliminates the mechanical 
vibration problem; (3) the elements of the cell are 
able to withstand greater force due to acceleration; 
(4) the whole cathode is illuminated, reducing vari- 
ation in sensitivity due to rotation of the fuze. Al- 
though the photosensitive surface is not normal to 
the incident light, it has been shown that the current 
produced by a given light flux does not vary appre- 
ciably with the angle of incidence, provided the sur- 
face is sufficiently “rough.” 


CONFIDENTIAL 


56 


DESCRIPTION OF PHOTOELECTRIC FUZE TYPES 



Figure 19. Cartridge-type photocells. View at upper 
left is 1P24 photocell in which cathode (top end) was 
integral with header. Others, except view in lower left, 
are experimental modifications to obtain smaller cell 
for more compact fuze. In lower left is photothyratron. 

5 5 ' 2 Sensitivity and Spectral Response 

Typical spectral response curves for three types 
of photosensitive surfaces are shown in Figure 20. 
The greater sensitivity of a cesium- antimony or S4 
surface indicates the desirability of its selection. In 
addition, although the light received by the photo- 



Figure 20. Spectral response curves of three typical 
photosensitive surfaces. 


cell in this application contains all wavelengths in 
the visible spectrum, light received at altitudes above 
5,000 ft is predominantly blue. 1 Thus the use of the 
cesium-antimony surface results in larger currents. 


Also there is less change in photocell current when 
the background changes from sky to clouds. 1 With 
the Cs-O-Ag surface, sensitive in the red, the sky 
appears dark; transition from, clouds to sky causes 
a decrease in the current, similar to that caused by 
the appearance of a target plane and results in 
premature functioning. 

In early cells using the Cs-O-Ag surface, it was 
necessary to use gas amplification to obtain suffi- 
cient currents with which to work. Difficulty was 
encountered with “electrical noise,” especially at 
low light levels. It was in some way connected with 
the charge accumulation on the glass envelope of 
the tube, and better performance was obtained by 
improving the electron optics of the assembly . How- 
ever, the electrical noise problem was very trouble- 
some until the cesium-antimony surface was 
adopted. 

The advantages of photocells with this type of 
surface are: (1) greater sensitivity; (2) reduced 
noise, since gas amplification is unnecessary; (3) 
low electrical leakage; and (4) reduced contrast 
between clouds and sky. 

The first cells made with the cesium-antimony 
surface were similar in construction to the first 
models, which had conical cathodes. They were fol- 
lowed by the more practical RCA-936 cartridge 
type of photocell with a flat cathode surface. A simi- 
lar photocell, the GL-516, which had essentially the 
same electrical and mechanical properties, was de- 
veloped by the General Electric Company. 

Improved technique in depositing the photosensi- 
tive surface, 103 ' 105 principally the removal of the 
cesium capsule from the photocell proper to a tubu- 
lar extension which was later sealed off, resulted in 
the development of the 1P24 (GL-564), which was 
approximately twice as sensitive 33 as any of the 
preceding types. [The GL— 564 experimental photo- 
cell became the 1P24 according to Radio Manufac- 
turers Association (RMA) nomenclature.] 

5 ’ 5 - 3 Construction 83 

The photocell consists of a cylindrical lime glass 
bulb to which are sealed assemblies mounted on 
headers of Allegheny metal. In preparing the bot- 
tom assembly, a nichrome cathode disk is welded to 
the header, which has been stamped from Allegheny 
55. After this assembly has been thoroughly cleaned 
to remove grease and surface impurities, the glass 
bulb and the tubulation are sealed to it. A layer of 


CONFIDENTIAL 



PHOTOCELLS 


57 


antimony is then deposited on the cathode disk in 
an extremely good vacuum. 

The top assembly consists of a similar Allegheny 
header to which is welded a nickel cup (see Fig- 
ure 19). A cesium pellet is placed in the cup and 
held there by a cover spot welded around the edge 
of the cup. This assembly is then sealed to the glass 
bulb. The tubulation is sealed to an exhaust system, 
and, after a preliminary bakeout at 275 F, the 
cesium pellet is flashed, depositing cesium on the 
antimony surface. Excess cesium is removed by fur- 
ther bakeout, and the tube is sealed off. 

An attempt was made to simplify construction 
by depositing the photosensitive surface directly on 
the Allegheny header. Cells of this type were less 
satisfactory, possibly because of the difference in 
base metals, and it was decided to direct efforts 
toward improvements in the other design. 

Further research by the General Electric Com- 
pany resulted in the development of a procedure for 
making cells nearly twice as sensitive as those of 
the preceding design. 

Instead of placing the cesium pellet in the nickel 
cup inside the photocell, it is placed in tubulation 
sealed to the anode header. After bakeout and flash- 
ing, the tubulation is sealed off beyond the location 
of the pellet. The cesium is then distilled into the 
photocell, where it strikes the cathode disk. Finally, 
the tubulation is sealed off hot as close to the anode 
header as possible. 

5,5,4 Detailed Properties 

1. Sensitivity. With 135 volts applied between 
anode and cathode, and light (color temperature 
2870 K) applied to the cathode, the response was 
required to be not less than 40 microamperes per 
lumen. 83 (The sensitivity of the 1P24 cells averaged 
75 microamperes per lumen.) 

It was found that the sensitivity remained re- 
markably constant under various conditions of stor- 
age and exposure. 

2. Gas content ( gas ratio) . When potentials of 250 
volts and 135 volts were applied between anode and 
cathode and light was incident on the cathode, it 
was required that ratio of currents at the two volt- 
ages not exceed 1.1. 91 

3. Cathode uniformity. With only a 90-degree 
sector of the cathode illuminated, it was required 
that as the cell was rotated, the ratio of the maxi- 


mum to the minimum currents should not exceed 
1.5. 94 

4. Leakage. With no light incident upon the cath- 
ode and 250 volts applied between cathode and 
anode through a 0.5-megohm resistor, it was re- 
quired that the current should not exceed 0.005 
microampere. 83 

5. Mechanical uniformity. The photocells were 
required to meet fairly rigid mechanical tolerances. 
For example, the plane of the cathode and the 
plane of the exterior seating shoulder were required 
to be parallel within 1 degree. 93 

5,5,5 Special Cells 

1. Gas- filled photocells. A number of photocells 
of the RCA-936 type were made with gas introduced 
to provide amplification. The average sensitivity 
of 27 cells tested at an anode voltage of 135 volts 
was 149 microamperes per lumen. However, when 
the manufacture of a very high sensitivity surface 
was accomplished (1P24), the need for a gas-filled 
photocell disappeared, and the research program was 
terminated. 

2. Special thyratrons. The development of a 
photothyratron 56 was undertaken in an attempt to 
replace the small gas-filled thyratron with a tube 
requiring no filament power. Since the fuze already 
incorporated an optical system, the use of a photo- 
cathode for the thyratron suggested itself. A num- 
ber of tubes which were made indicated that a thy- 
ratron could be developed to function when a rea- 
sonable quantity of light fell on the cathode. These 
tubes, designated as the RCA C-7071, were essen- 
tially gas-filled photocells of the cartridge type with 
a grid mounted between the anode and the cathode 
surfaces (see Figure 19) . Although the good photo- 
thyratrons were capable of passing the large cur- 
rents required, they presented three major disad- 
vantages: (1) the critical grid firing voltage was 
dependent on the cathode illumination; (2) it was 
difficult to prevent photoemission from the grid; (3) 
large currents, if repeated many times, damaged the 
cathode surface. Therefore, attention was turned 
toward the development of a cold-cathode tube. 
Electrical characteristics of these tubes are given in 
reference 109. 

Several cold-cathode thyratrons (R-6236) were 
designed and made, taking advantage of the rigid 
cartridge photocell construction. The tubes devel- 


CONFIDEN 


58 


DESCRIPTION OF PHOTOELECTRIC FUZE TYPES 


oped were more sensitive and better constructed 
than preceding tubes of the cold-cathode type, but 
they operated on a positive grid voltage of about 
70 volts, making them less desirable than the fila- 
ment-powered thyratrons used in the T-4 fuze. 

3. Small photocells. Two sizes of small photocells 
were constructed in an effort to make the fuze more 
compact (see Figure 19) . One size was V 2 in. in 


diameter and 2 %2 in. in length, while the smaller 
was % in. in diameter and 15 / 32 in. in length. All 
cells had high sensitivities and appeared to be satis- 
factory. Average values are given as follows: 


Sensitivity Uniformity 
(|aa per lumen) (percent) 
Larger cells 102.7 87.9 

Smaller cells 93.0 74.3 


Gas ratio 

1.03 

1.04 


^CONFIDENTIAL 


Chapter 6 


LABORATORY METHODS FOR TESTING T-4 FUZES 
AND COMPONENTS a 


61 INTRODUCTION 

rp he primary aim of the laboratory tests of fuzes 
is to predict their operation when fired on mis- 
siles, in order to insure reliable performance. Be- 
cause of the wide variation in operating conditions, 
limits for the test must necessarily cover extreme 
ranges. Although simulation of field operations is a 
primary aim, ease of performing any given test is 
also of great importance. The most important over- 
all test for predicting field operation is the sensitiv- 
ity test. Other general tests are as follows: arming, 
noise, critical bias, vibration, jolt, temperature and 
humidity, and mechanical. Furthermore, specific 
tests have been performed on photocells, lenses, non- 
linear resistors, and pentode tubes. 

62 SENSITIVITY TESTS 

621 Dropping Ball Method 1 

The first type of sensitivity test which compares 
with field operations is one in which a falling ball 
simulates the target, passing the field of view of the 
lens. In the actual test, the distance between the 
fuze and path of the ball was chosen so that the 

a This chapter was written by P. J. Franklin of the Ord- 
nance Development Division of the National Bureau of 
Standards. 


falling ball would have the velocity required to give 
a pulse of the right duration to correspond to the 
missile’s passing the target. Black balls of increasing 
size were dropped until the thyratron fired, as indi- 
cated by a neon bulb connected to the thyratron. 
This process was repeated until the fuze fired on a 
ball of given size 5 successive times but not on the 
ball of next smaller size. Sensitivity was calculated 
in terms of percentage of total light obscured by the 
ball. The test was usually performed out of doors 
in order to provide uniform light intensity of proper 
magnitude on the photocell. 

The falling ball method of determining sensitiv- 
ity was at best a slow and tedious process, and 
faster methods were sought. 

Mechanical Chopping 2 

The next modification of the sensitivity test in- 
volved the use of two lamps, one behind the other, 
with a chopping bar between them. The apparatus 
consisted essentially of: two lamps, one for the 
signal and the other to produce the required light 
level; a system of lenses; and a high-speed cam- 
operated shutter to produce a sharp cutoff of the 
light from the signal lamp. A schematic diagram of 
the setup is shown in Figure 1. 

The signal was varied by using combinations of 



Figure 1 . Schematic method of measuring PE fuze sensitivity by light chopping. Lens of fuze, on which light is 
focused by lens L s , is shown at left. Light source & provides background illumination, and source Si (focused on S2 ) 
provides fractional light level which is momentarily cut off by cam-operated shutter. 


CONFIDENTIAL 59 


60 


LABORATORY TESTING OF T-4 FUZES AND COMPONENTS 


five wire screens with different meshes. The screens 
were calibrated with a blue-sensitive vacuum cell 
(RCA-7052) mounted in a regular fuze assembly. 
Transmissions, measured with various combinations 
of screens, checked reasonably well with the values 
computed from the individually measured transmis- 
sions. A table of per cent signal for various screen 
combinations was then prepared from the various 
transmissions. If T is the screen transmission; i, the 
value of the photocell current from lamp S 2 ; and i 8 , 
the value of the current from lamp S, with no screen ; 
then the signal, <S, expressed as a fraction of the 
initial light level before the signal light cuts off, is 


Ti s ^ Tig 
1 Ti 8 i 


( 1 ) 


for small signals. Reasonably good agreement was 
obtained by the method with computed sensitivities 
based on the photocell characteristic. 

A few important points in the design and use of 
the apparatus should be mentioned. 

1. Either the per cent signal adjustment or the 
light level adjustment, but not both, may be made 
by means of an iris diaphragm. If a diaphragm is 
used for one adjustment, then the other must be 
made by alternating the beam over its whole cross 
section. Otherwise, the light level and per cent sig- 
nal will not be adjustable independently of one 
another. 

2. The shutter mechanism must be isolated me- 
chanically from the optical system to avoid serious 
microphonic effects from the lamp filaments. 

3. The effective angle subtended by lenses L 3 at 
the lens of the unit under test must be smaller than 
the angular width of the field of the latter lens. 

4. A very steady source of direct current, such as 
a storage battery, must be used for lamp filaments. 

5. The shutter must have a rough blackened sur- 
face to prevent reflection effects from the lamp S 2 . 
This is important for small signals. 

6. The effect from bouncing of the shutter must 
be eliminated by allowing ample motion after cutoff, 
or providing a friction catch. A half-inch extra 
motion after cutoff was found to be sufficient. 


6 . 2.3 Modulated Lamp Apparatus 23 

Although pulse tests for sensitivity were the most 
reliable method for obtaining design data, they were 
too time-consuming for production or quality con- 


trol purposes. A rapid and reasonably reliable sen- 
sitivity test used a light source which was modulated 
with a known percentage of 60-c alternating cur- 
rent. The amount of modulation was increased until 
the thyratron of the fuze was triggered. 

The lamp and fuze were mounted as shown in 
Figure 2. A set of screens was used for varying the 


SCREEN HOLDER 



Figure 2. Schematic arrangement for measuring sen- 
sitivity of PE fuzes with modulated source (lamp). 
Overall light level is controlled by screens between 
fuze and source. 

light level in steps. The per cent light signal was 
controlled by the a-c modulation of the lamp and 
was independent of the level seen by the fuze. For 
the particular lamp used, the per cent light modula- 
tion was approximately % the per cent voltage 
modulation. When the lamp was operated at its 
normal voltage, it aged rather rapidly, and, for a 
given voltage modulation, the per cent light signal 
might increase markedly after a few hours. This 
effect of decreasing thermal inertia of the lamp ac- 
counted in one instance for errors up to 25 per cent 
in threshold (inverse sensitivity) measurements. 
The diagram of the lamp circuit is shown in Fig- 
ure 3. 

To calibrate the modulating source, a standard 
fuze head containing a photocell and lens assembly 
was mounted so that it viewed the source at an 
angle of 22.5 degrees (see Figure 4). A pair of 
shielded leads connected the photocell to an attenu- 
ator box containing a battery, connections for a 
microammeter to read photocurrent, and a cali- 
brated, noninductive, continuously variable resist- 
ance. The output from this circuit was connected by 
a shielded cable to one input of a high-gain ampli- 
fier. A standard 60-c signal, ordinarly 1 volt (rms) , 
was applied to another input of the same amplifier. 


CONFIDENTIAL 


SENSITIVITY TESTS 


61 




Figure 3. Circuit for controlling percentage light modulation of lamp shown in Figure 2. 


Inside the amplifier there was provided a calibrated 
10,000-ohm step attenuator for the standard signal. 
The attenuator was ordinarily used at 1/10,000, 
giving a 0.1 -millivolt standard input to the ampli- 
fier. The input impedance of the amplifier was 5 
megohms, which was high enough so that there was 
no observable loading effect of the amplifier on 
either the standard source or the photocell circuit. 
This precaution was important. 

The actual calibrating procedure follows: The 
standard source was set at 1 volt (rms). With the 
input selector on Number 2 (Figure 4) and the in- 
put attenuator at 1/10,000, the gain control was 
adjusted until the oscilloscope showed a conveniently 
readable deflection, for example, 10 divisions. The 


d-c lamp voltage was then set at the proper point 
(see following paragraph on light level calibration) , 
and the Yariac (Figure 3) was set at some arbitrary 
reading at which it was desired to calibrate. This 
was more convenient than using an a-c voltmeter to 
read the modulation and was proper, provided the 
line voltage was controlled. The gain control was 
left fixed, and, with the input selector on Number 1 
(Figure 4) , the photocell series resistance was varied 
until the oscilloscope reading had returned to the 
value at which it was set. The input to the amplifier 
was then 0.1 millivolt (rms), and the photocurrent 
ripple was, therefore, 10" 4 /.R, where R was the re- 
sistance in the photocell circuit. If I is the current 
reading of the microammeter, then the “fractional” 


i 

1 



Figure 4. Schematic setup for calibrating modulated light source (Figure 2) used for measuring sensitivity of 
PE fuzes. 


CONFIDENTIAL 


i 


62 


LABORATORY TESTING OF T-4^ FUZES AND COMPONENTS 


light signal is 10 ~*/RI (rms). The peak per cent 
signal is then by definition equal to 100 \/2 times 
this value. A typical calibration curve is shown in 
Figure 5. 



Figure 5. Calibration of modulated lamp in terms of 
Variac setting (Figure 3). 


Threshold measurements had to be carried out 
over a range of light levels which covered approxi- 
mately the expected range of operation of the unit. 
As light conditions and photocell sensitivities varied 
widely, it was necessary to define a reference light 
level in terms of some kind of standard source. 20 ’ 21 

Preliminary to this, a set of standard heads (cell 
and lens in regular fuze noses) were made up with 
cells having sensitivities in the neighborhood of 25 
to 30 microamperes per lumen. 23 These were used 
for light measurements under various conditions to 
determine the range of values likely to be encoun- 
tered. Variations of light level with time of day and 
altitude are discussed in Chapter 4. 

For tentative standardization, a representative 
light level, L 0 , was defined as the level which would 
produce a current of 8 microamperes in a representa- 
tive standard cell-lens assembly containing a cell 
with a sensitivity of 30 microamperes per lumen. 
The levels at which thresholds were to be measured 
were 0.05L o (below which the unit rapidly became 
insensitive), L 0 , and 3 L 0 . The last level was high 
enough to allow for fairly extreme conditions of high 
light level, including a probable increase in cell sen- 
sitivity, as manufacturing technique improved. 

Originally the light level L 0 was defined in terms 
of photocell current. Since photocell sensitivities 
changed gradually with time, the level L 0 was later 
defined in terms of photometric standards by the 
Bureau of Standards Photometry Section. The stand- 


ard light level L 0 could be suitably defined as that 
level for which the light flux from a standard lamp 
at the surface of the lens was 0.75 lumen per sq cm 
and in such a direction that the photocurrent in the 
cell was a maximum. 

The threshold of a fuze was defined as the peak 
percentage modulation of the light signal required 
to trigger the thyratron. This depended on the form 
and duration (or frequency) of the signal, and, with 
the modulated light apparatus, referred to a 120-c 
sinusoidal signal. The peak per cent modulation 
referred to the maximum departure from the mean 
light level, expressed as a percentage of the mean 
level. Thus, in the case of the sinusoidal signal, the 
peak signal denoted one-half the peak-to-peak value 
rather than the total fluctuation. 

63 OPERATING TESTS 

The operating tests on the MC-380 assembly con- 
sisted of measuring: (1) threshold (by the modulated 
lamp method), (2) stability at arming, (3) electri- 
cal noise, and (4) self-destruction [SD] time. These 
tests were made in a single test position, using a test 
circuit as is shown in Figure 6. The terminals of the 
MC-380 adapter are as indicated in Figure 5 of 
Chapter 5. 

The MC-380 nose was powered by voltages from 
large-capacity batteries in the test circuit rather 
than from a fuze battery. However, provision was 
made to use, for special tests, a fuze battery (lower 
right, Figure 6) . The switches marked S were ganged 
together and when closed, put the test equipment in 
operating condition. The switches marked SI were 
also ganged, and, when these were closed, power was 
supplied to the fuze circuit, initiating the arming 
cycling. The clock was also started to measure SD 
time. The switches S2 had to lie in position of the 
arrows in order for the SD circuit to be effective. 
SD was always measured first in order to obviate 
the possibility of erroneous values being obtained 
from residual voltages or the capacitors in the SD 
circuit. 

Voltage was applied to the thyratron plate by 
a 0.1 -microfarad capacitor charged through a 0.5- 
megohm resistor from the B supply. When the 
thyratron was triggered, the condenser discharged 
through the thyratron in series wfith a 10-ohm re- 
sistor (simulating the resistance of the electric 
detonator). Firing was indicated by the lighting of 


CONFIDENTIAL 


SERVICE TESTS 


63 



SUPPLY 

Figure 6. Circuit diagram of operating test position for T-4 fuzes. With fuze nose (MC-380) plugged into termi- 
nals (upper left), measurements were made of threshold, noise, stability at arming, critical bias (of fuze thyratron), 
and SD time. 


a flashlight lamp. This was operated by a relay 
which was energized by the pulse across the 10-ohm 
resistor. An inverter stage and auxiliary thyratron 
in the test circuit coupled the resistor to the relay. 
A contact on the same relay was available to stop 
the clock in order to give an automatic measure of 
SD time. Firing of the thyratron prior to the proper 
range of SD times indicated a defective unit. After 
the SD was measured, the S2 switches were shifted 
to the position away from the arrows, rendering the 
SD circuit inoperative and disconnecting the clock. 

The arming test was accomplished automatically 
by means of a time delay circuit and another 885 
thyratron, which operated a relay and closed the 
thyratron plate circuit at an adjustable time after 
closure of filament and plate circuits. Firing of the 
thyratron at the end of the arming time delay indi- 
cated failure of the unit to arm properly. 

The noise test was performed by setting the thy- 
ratron grid bias at — 4 volts ( — 6 volts was the nor- 
mal operating value). If the unit fired within a 
specified time limit (30 sec) , it failed the noise test. 

The threshold measurements were made by set- 


ting the light level at the desired value, resetting 
the filament plate and bias voltages at the desired 
values, and turning up the light signal slowly by 
means of the Variac control (Figures 2 and 3), until 
the unit fired. The per cent threshold for this light 
level could then be read from the calibrating curve 
for the per cent signal against Variac reading (Fig- 
ure 5) . 

A critical grid bias test was made to determine the 
margin of safety between the noise level and the 
signal required to fire the unit. A motor-driven po- 
tentiometer placed across the C bias circuit grad- 
ually reduced the bias until the fuze fired. The 
discharge of the thyratron operated a relay which 
stopped the motor and permitted a reading of the 
bias voltage to be taken. 38 The difference between 
this value and the normal bias gave the holding bias 
for the fuze. 

64 SERVICE TESTS 

A number of tests were made to determine the 
ability of the fuze to stand up under various service 


CONFIDENTIAL 


:al 


64 


LABORATORY TESTING OF T-4 FUZES AND COMPONENTS 


conditions. These tests included vibration, jolting, 
and temperature and humidity cycling. Mechanical 
gauging tests were also made to insure that the fuze 
could be installed properly in the rocket. 

The vibration test gave an indication of the micro- 
phonic stability of the vacuum tubes. It also served 
to show up defective workmanship, such as poorly 
soldered connections and insecure anchoring of parts 
(sometimes due to incomplete potting). A commer- 
cial vibrator was used (Vibratron by American Tool 
and Instrument Co.). The frequency of vibration 
was selected to correspond to the frequency of maxi- 
mum gain of the amplifier. The amplitude of vibra- 
tion was % 4 in. An excessive or spurious signal at 
the thyratron grid (observed on an oscilloscope) led 
to the rejection of a fuze. 

Samples of fuzes from production lots were re- 
quired to withstand a standard Ordnance Depart- 
ment jolt test. The test was primarily intended to 
check the safety of the arming mechanism of the 
fuze, but it also gave an indication of the ability 
of the fuzes to withstand rough handling. 

Temperature cycling tests involved storage at 
— 40 C for 48 hours followed by another 48 hours 
at -|-60 C. The electronic assemblies were re- 
quired to be in operating condition after such 
exposure. Occasionally, units would fail due to de- 
fective potting. The wax potting compound was 
liable to shrinkage at the low temperatures and 
sweating at the high temperatures. Careful control 
of the potting process was necessary to avoid trou- 
bles from these causes. 

Resistance of the fuze to high humidity was deter- 
mined by water immersion tests. Units were required 
to be in operating condition after immersion in water 
at room temperature for 4 hours. 

In addition to gauging of the threads and dimen- 
sions, mechanical tests included strength tests on 
the contact pins of the base of the electronic as- 
sembly, and center of gravity measurements. The 
latter served primarily to show up voids in the pot- 
ting process. 

65 PHOTOCELL TESTS 

6,5,1 Electrical Tests 

The following properties of the photocell were 
determined by electrical tests: sensitivity, spectral 
response, uniformity, gas multiplication, and dark 
current. A noise test, originally planned as a routine 


test procedure, revealed that only about 0.1 per 
cent of the first 3,000 cells produced were noisy, and 
it was discontinued. The electrical tests were all 
made in a single test setup shown schematically in 
Figure 7. The control panel is shown in Figure 8, 
and the wiring of the photocell circuit is shown in 
Figure 9. Full details of the equipment are in ref- 
erences 30 to 36, inclusive. 



STANDARD 

PHOTOCELL 

MOUNT 

Figure 7. Schematic diagram of arrangement for 

calibrating photocells used in T-4 fuzes. 

The light source (lamp, Figure 7) was a 32-candle- 
power, 6-8 volt, double-contact, bayonet connection, 
automobile lamp, mounted in a standard lamp 
socket. A supply of these lamps was calibrated by 
the Optical Section of the National Bureau of 
Standards giving: (1) the current at which the lamp 
had to be operated in order to secure a color temper- 
ature 2870 K, and (2) the candlepower of the lamp 
at this current. Soldered connections to the lamp 
were necessary to prevent current fluctuations. The 
energy for the lamp was supplied by an external 
storage battery. 

The mount for the photocell under test was so 
located that the center of the cathode of the cell 
was approximately 4 in. from the center of the fila- 
ment of the lamp. In order to be able to test the 
uniformity of the photocell in different directions, 
the photocell mount could be rotated by means of a 
flexible shaft connected to a knob at the front of 
the panel (Figure 8) . 

A baffle screened the entire photocell from direct 
illumination, except for an elliptical beam which 
illuminated the cathode; this beam extended just 
far enough outside the cathode to insure that the 
cathode was entirely illuminated. 

A shutter was provided so that a 90-degree sector 





PHOTOCELL TESTS 


65 



+ o 

b l - battery 

CONNECTIONS 

-O 


S v : VOLTAGE 
SELECTOR SWITCH 


ft 


S p : STANDARD 

PHOTOCELL 
SELECTOR SWITCH 


ft 


R c !COARSE 
LAMP CONTROL 



+ o 

I L AMMETER 
CONNECTIONS 

-o 


r p 


©y 


MICRO-AMMETER^ 

CONNECTIONS 



o 

Q X 

<z o 


o 

x 

o 


£ 

(/) 


CL 

2 

< 


O 

x 

o 


* 

CO 



o o 

SHUTTER 

CONTROL 


<o' 


R f *-FINE 

LAMP CONTROL 




\ ROTATION 
' CONTROL / 


Figure 8. Diagram of control panel for apparatus used to calibrate photocells. 


of the cathode could be illuminated. The shutter 
could be placed in or withdrawn from the beam 
by means of a control lever at the front of the 
panel. 

In the design of the photocell circuit, care was 
taken to insure that no leakage in the circuit itself 
would be indicated on the microammeter. The elimi- 
nation of such currents was important in measuring 
conduction at very low or no illumination. The test 
cell and the standard cells were so connected in the 
circuit that any leaks across insulators were shunted 
to ground without passing through the meter. 
Shielded cables were used. 

In addition to the photocell under test, three 
standard photocells were mounted in the apparatus 
for use in adjusting the lamp intensity. When a 
lamp was installed, it was operated at the specified 


color temperature as indicated by the ammeter, and 
the photocurrents flowing in the standard photocells 
were observed. Thereafter, the lamp was regulated 
by setting the standard photocell currents. This 
assured constancy of the light flux from the lamp. 
Three standard photocells were used to permit a 
check. A marked disagreement between the lamp 
current and the standard photocell current indicated 
a deterioration of the lamp; it was then necessary 
to replace the lamp. The fact that the photocells 
used as standards were of the same type as those 
under test nullified largely any change in lamp 
characteristics. The standard photocells had voltage 
applied only when they were actually in use; only 
22.5 volts were used on the standard cells. These 
precautions were intended to prevent deterioration 
of these photocells. The standard photocells were 


CONFIDENTIAL 


66 


LABORATORY TESTING OF T-4 FUZES AND COMPONENTS 


selected for average sensitivity, high uniformity, low 
gas multiplication, and low dark current. 

An accurate measurement was made of the dis- 
tance from the lamp filament to the center of the 
rim of the cathode of the photocell in the test cell 
mount. From the geometry of the setup and the 



PHOTOCELL CIRCUIT 



LAMP CIRCUIT 

Figure 9. Wiring diagram of photocell circuits of 
Figure 7, showing shielding, switches, meters, and 
batteries. Pi, P 2 , and P 3 are reference photocells, and 
Pt is cell under test. 

candlepower of the lamp, the quantity of light il- 
luminating the cathode could be evaluated. The 
sensitivity of the photocell could thus be determined 
from the measured photocell current and the calcu- 
lated quantity of light on the cathode. 15 

All requirements specified for the various tests 
were to be met after the photocell had been stored 
in darkness for at least one week (corresponding to 
probable field service conditions for the fuzes) . The 
test for sensitivity was to be made immediately 
after the photocell had been removed from dark 
storage. The light incident upon the tube after re- 


moval from darkness and prior to this test was 
never to exceed an equivalent of 10 footcandles 
for 1 minute. All remaining tests were to follow the 
sensitivity test. 29 

The test of sensitivity was repeated with a Corn- 
ing signal red filter (4.0 =±=0.1 mm in thickness) 
introduced into the light beam. The response with 
this red filter was not to exceed 10 per cent of the 
response without a filter. 

A sampling procedure was adopted to apply to the 
cells used for this test. Twenty sample photocells 
were selected at random from each day’s production. 
If more than one photocell failed the test specified, 
an additional sample of 80 cells was selected and 
tested. If more than a total of 5 photocells from 
both samples failed, the entire day’s production was 
tested, and the photocells failing the test were 
rejected. 29 

Uniformity Measurement ( Sensitivity Distribu- 
tion) . Uniformity was very important in the earlier 
types of photocells since the lens system focused 
light from each section of the sky upon a small area 
of the cell. Lens systems that were developed later 
(T-4 fuze) focused light from all radial directions 
over the entire cathode, and nonuniformities of the 
cathode surface were less important. 

In order to measure uniformity, the test for sen- 
sitivity was repeated, except that the shutter was 
brought into the beam; an opaque sector in the 
beam of light was thus provided so that only a 90- 
degree sector of the cathode was illuminated. The 
opaque sector was so oriented that its central radius 
was perpendicular to the direction of the beam. As 
the photocell was rotated about its axis through a 
complete revolution, the maximum and minimum 
photocurrents were observed. The uniformity was 
defined quantitatively as the ratio of the minimum 
to the maximum sensitivity. It was required that the 
ratio of the maximum to the minimum photocurrents 
not exceed 1.5. 

Gas Multiplication Measurement. Tests over long 
periods of time showed that a cell might be rela- 
tively free from gas for several months and then 
become too gassy to be used. Any gas leakage at the 
time of the test seemed to be a sufficient cause for 
rejection. 

In order to measure gas multiplications, the test 
for sensitivity was repeated with the cathode com- 
pletely illuminated. The photocell current was ob- 
served when the voltage applied between the anode 


CONFIDENTIAL 


LENS TESTS 


67 


and the cathode was changed from 135 to 250 volts. 
The ratio of the currents was specified as not to 
exceed 1.1. 

Dark Current Measurement. The electrical leak- 
age test could not be made satisfactorily during 
damp weather due to the leakage on the outside of 
the glass, representing no defect of the photocell 
itself. 15 If a photocell displayed an unsatisfactorily 
large leakage, it was not to be discarded until it was 
clear that this was not due to conductance on the 
outside of the glass. 

For dark current measurements, the lamp was 
extinguished, and the current was observed when a 
potential of 250 volts was applied to the anode 
through a 0.5-megohm resistor. The small current 
could be detected by noting any motion of the meter 
needle when the voltage was turned off. The current 
was not to exceed 0.005 microampere. 29 


6,5,2 Visual Inspection and Mechanical 
Tests 15 


6 6 LENS TESTS 

A good magnifying glass with a magnification 
factor of about 4 was used to detect flaws in the 
surface, the slit, and the paint of the lens. A simple 
light source was used for inspecting the completed 
lens assembly to determine the position of the photo- 
cell and any obstructions in the field of view. A 
sketch of this apparatus appears in Figure 10. The 


LAMP SOURCE (60 WATT) 



LENS ASSEMBLY 
(PROFILE VIEW) 


Figure 10. Schematic arrangement used to examine 
lenses in T-4 fuzes. 


The photocells were subjected to visual inspec- 
tion. Loose dirt on the inside and stains on the glass 
were to be noted. It was important that the bulb 
be sealed to the headers without excessive wrinkling 
of the glass, that the glass be free from flaws, and 
that the headers be accurately placed. 

Gauges were constructed in order to check the 
accuracy of construction in certain respects. 15 

It was required that the angle between the plane 
of the cathode and the plane of the seating shoulder 
be checked by mechanical measurement before the 
photocell was sealed. The planes were specified to be 
parallel within 1 degree. The same sampling proce- 
dure used for testing spectral responses was to apply 
to this test. 

At the seal of the bulb to the cathode header, the 
glass was not to overhang beyond the edge of the 
header. No part of the photocell was to extend be- 
yond a distance of 0.458 in. from the axis of sym- 
metry of the cathode header. 29 

The photocell was expected to satisfy all electri- 
cal and mechanical requirements after centrifuging. 
The photocell, mounted in any position, was to be 
spun in an approved centrifuge. The cell was to be 
subjected to a force of not less than 2,500g, com- 
puted for the midpoint of the photocell. This test 
was made on a sampling basis. 


lamp projected a source of light into the lens at a 
forward angle of approximately 22.5 degrees. The 
observer could view the cathode from the equiva- 
lent position on the opposite side. The lens and 
photocell assembly could be rotated through an 
angle of 360 degrees. 

Tests of angular distribution of the field of view 
of the lens were made with the apparatus shown in 
Figure 11. The lens assembly, or fuze, was mounted 
at F. A stick was pivoted about a center, C, at the 
lens assembly, transcribing an arc, graduated from 
0 to 90 degrees. The 0-degree mark, located in a 
plane perpendicular to the fuze axis, passed through 
the center of rotation. A lamp S was mounted on the 
stick, one meter from the lens. A slit in front of the 
lamp restricted the light beam at the lens to an 
angle no greater than 0.2 degree in the plane of the 
arc. The lens could be rotated about the fuze axis 
with the photocell fixed, and the cell could be ro- 
tated with the lens fixed. The photocell was mounted 
permanently; lenses were removable. The photocell 
was connected to a 135- volt battery through a 
microammeter and a series resistance. Another 
method consisted of using an a-c lamp source and 
measuring the photocell output with an a-c galva- 
nometer. 

Lenses in completed fuzes were tested by apply- 


CONFIDENTIAL 


68 


LABORATORY TESTING OF T-4 FUZES AND COMPONENTS 


ing 110 volts a-c to the proper terminals on the base 
plate of the fuze nose through a d-c microammeter 
or galvanometer with a protective resistance in se- 
ries. The meter measured the rectified photocurrent. 



Figure 11. Arrangement used to measure field of view 
of lens-slit system of T-4 fuzes. 

The photocurrent was not actually proportional 
to the light intensity since, during part of the a-c 
cycle, the photocell was operating below the satura- 
tion point on its current-voltage characteristic. 


However, by comparing the a-c meter readings 
against d-c, a calibration for the a-c method was 
obtained. For example, the 50 per cent transmission 
point with d-c voltage might be at 52 per cent with 
a-c. 

67 TESTS ON NONLINEAR RESISTORS 

Resistance measurements were made of the criti- 
cal values (discussed in Section 5.4) of the nonlinear, 
photocell-load resistors. Ordinary high-resistance 
measuring circuits were used. In addition, the load 
resistors were examined for self-noise. 

Since the fuze was designed to operate on a change 
of light level of approximately 1 per cent, the speci- 
fication for maximum noise level in the load resistor 
was set at a value equivalent to a 0.1 per cent light 
signal. The noise level was determined by passing a 
current of 10 microamperes through the resistor and 
amplifying the random voltage changes with a prop- 
erly shaped amplifier. The pulses could then be ob- 
served on an oscilloscope, or could be used to trigger 
a thyratron, which would indicate if the resistor were 
noisy. 

68 PENTODE TUBE TESTS 

Traces of gas were found to be present in vacuum 
tubes after long periods of storage. The input imped- 
ance of the fuze amplifier was lowered by a large 


cs 




PENTODE TUBE TESTS 


69 


factor in the presence of such traces of gas. 6 The 
presence of gas in pentodes after long periods of 
storage, moreover, set a practical limit on the mag- 
nitude of the input impedance of the amplifier. 12 * 16 
The input impedance of the pentode tubes was 
measured by means of the test circuit shown in 
Figure 12. A 10-megohm resistor was connected in 
series with the input grid. Readings were obtained 
for the output voltage with and without the 10 meg- 
ohms shorted. 18 Using a 0.6- volt (rms) , 100-c input, 


the voltage output of the stage was specified to be 
in the range 1.5 to 7.5 volts (rms) at all times be- 
tween 2 sec and 30 sec following the application of 
voltages for the first time. 28 (The definition of “first 
time” was any time following shipment, subject to 
the time limit specified, assuming that no voltages 
had been applied to the tube since the final factory 
testing process.) These tests were not to be made 
sooner than 72 hours after the final factory aging 
process. 




CONFIDENTIAL 


Chapter 7 

FIELD TEST METHODS FOR PE FUZES 


71 INTRODUCTION 

T he types of field tests may be classified as 
follows: 

1. Performance tests: to determine the reliability 
and sensitivity of the fuze under standard condi- 
tions. 

2. Effectiveness tests: to determine damage effec- 
tiveness. General considerations for effectiveness 
tests on proximity fuzes are given in reports on 
radio fuzes b and are applicable to all proximity 
fuzes. No special techniques have been developed 
for effectiveness tests with photoelectric fuzes. 

3. Radio reporter tests: use of special units con- 
taining radio transmitters to determine behavior of 
the fuze, fuze components, or the missile during 
flight. A more common name would be tele- 
metering. 

4. Miscellaneous: other tests such as arming dis- 
tance tests and sunfiring tests. Test procedures on 
these tests will be discussed as needed in Chapter 8 
of this volume, which deals with fuze perform- 
ance. 

The main part of this chapter deals with the per- 
formance tests. The principal considerations in plan- 
ning these tests were: 

1. Provision of adequate safety precautions. All 
tests were made with inert-loaded projectiles. The 
operation of the fuze was indicated by a spotting 
charge. 

2. Provision of means for quantitative measure- 
ments of results. Visual observations and photo- 
graphic records were made of the burst positions. 
Principal reliance was generally placed on readings 
from the photographic films. 

3. Simulation of combat use. This involved selec- 
tion of suitable targets and firing conditions. Firing 
of rockets from the ground against a stationary 
target was suitable for simulating combat fire since 
it gave the same velocity of fuze relative to target 
as plane-to-plane pursuit fire for planes moving at 
approximately equal speeds. 

a This chapter was written by Alex Orden of the Ordnance 
Development Division of the National Bureau of Standards. 
b See Division 4, Volume 1. 


70 


7 2 TESTS ON BOMBS la 

Four types of field tests (not including reporter 
tests) were made during the bomb fuze develop- 
ment: 

1. Flyover tests. Fuzes were mounted on a rack 
on the ground, and an airplane was flown over them 
at various heights. These tests were of considerable 
value in determining fuze sensitivity. They gave no 
information on fuze reliability since the fuzes were 
not subject to the vibration or background light 
variations of a bomb in flight. 

2. Free fall tests. Fuzes were mounted on bombs 
and dropped from an airplane. No target was used. 
This tested reliability but gave no information on 
sensitivity. The fuzes were detonated by self- 
destruction before they reached the ground. 

3. Airborne target tests. Fuzes mounted on bombs 
were dropped against towed sleeves and against 
drones. Photographs from the bombing plane, the 
tow plane, or drone control plane, and from an addi- 
tional observation plane provided data for determin- 
ing burst positions. 

4. Ground approach tests. Some fuzes mounted on 
bombs were dropped over wooded terrain and a few 
other types of terrain. The heights of function were 
estimated visually. 

7 3 TESTS ON ROCKETS FIRED FROM A 
PLANE 

The proving ground tests of photoelectric fuzes 
mounted on rockets may be divided into plane-firing 
tests and ground-launched tests. In order to facili- 
tate observation of burst positions and trajectories, 
the rounds fired from airplanes were directed against 
stationary balloons. The balloons were of black rub- 
ber and were sausage-shaped, 5 ft in diameter and 
15 ft long (see Figure 1). They were moored at 
heights of 150 to 500 ft. Rocket dispersion was high, 
and, in order to improve the probability of the fuze 
passing within operating distance of a target, sev- 
eral balloons were used simultaneously in some of 
the tests. Some difficulties were encountered with 
ground light variations. This problem was eliminated 
by raising the targets over water instead of land. 


CONFIDENTIAL 


TESTS ON ROCKETS FIRED FROM THE GROUND 


71 



Figure 1 . Target balloon for plane-firing tests. 


Observations were made visually and photographi- 
cally from stations on the ground. The bursts were 
indicated by smoke puffs. Some of the rockets were 
provided with smoke tracers to show the trajectory. 
The rocket launching tubes are shown in Figure 2. 



Figure 2. Rocket launching tubes on wing of P-40. 


7 4 TESTS ON ROCKETS FIRED FROM 
THE GROUND 

There were three kinds of rocket firing from, the 
ground : 

1. High-angle firings (30 to 60 degree elevation) 
against a stationary target. 

2. Horizontal firings (0 to 10 degree elevation) 
against a stationary target. 

3. High-angle firings for ground approach func- 
tion. 

In the high-angle firings, the target generally used 
was a black balloon 12 ft in diameter. It was moored 
to the ground and tied to a barrage balloon above 


«iSs 



Figure 3. Barrage balloon and 12-ft diameter spheri- 
cal target balloon for photoelectric rocket fuze tests. 


it. The target balloon and barrage balloon are 
shown in Figure 3. A cloth panel assembly, which 
presented a target aspect 9x18 ft, was also used. It 
was hung from the barrage balloon and also moored 



Figure 4. Launcher for 3%-in. practice rockets for 
photoelectric fuze tests. 


to the ground. The launcher was a rail assembly or 
tube mounted on a swivel base (Figure 4). It was 
necessary to aim the launcher on each round as the 
target shifted in the wind. The elevation varied 
from 30 to 60 degrees and the range from 1,000 to 



72 


FIELD TEST METHODS FOR PE FUZES 


2,000 ft. In some of the early tests, the rockets were 
equipped with tracers to show the flight paths. Fuze 
functioning was indicated by a smoke puff (Fig- 
ure 5) . The bursts were located relative to the target 



Figure 5. Smoke puff indicating fuze function against 

target. 

by trigonometric calculations based on photographs 
and transit measurements from two observation 
posts. Although function shown in Figure 4 appears 
to be beyond the target, it is actually slightly ahead 
of it. 

On horizontal ranges, the target was hung be- 
tween poles at a height of about 75 ft. The targets 
used were: (1) large targets consisting of many 
strips of black cloth hung from a fishnet or ropes 
(Figure 6) (these generally provided a target pulse 
well above the fuze threshold) ; (2) small targets 
consisting of a single black panel assembly, which 
provided threshold pulses; (3) a series of panels of 
increasing target aspect, spaced about 100 ft apart 
along the trajectory. 12 * 15 

The following is a description of a four-target 
array set up at Blossom Point Proving Ground. The 
first target was a black panel, 3x4 ft, on a pole 75 ft 
to the right of the line of fire. The target was in a 
vertical plane parallel to the rocket trajectory. It 
was 75 ft above the ground and was intended to be 
high enough to obscure sky light from the fuze, i.e., 
to be above the rocket trajectory. The pole was 900 
ft from the rocket launcher. This was about 200 ft 
beyond the arming point for 0.7-sec arming switches 
The second target was a similar panel, 4x11 ft on a 
pole 100 ft farther from the launcher. The third and 
fourth targets were each horizontal panels hung 
from ropes between poles. The rockets were in- 
tended to pass 30 ft below these targets. The third 
was 3x5 ft with a short side parallel to the trajec- 


tory and was 100 ft beyond target No. 2. The fourth 
was 3x10 ft and was 100 ft beyond target No. 3. 

For average trajectories 75 ft to the left of the 
first two targets and 30 ft below the last two targets, 
the peak target obscurations were calculated to be 
0.9, 1.8, 3.5, and 7.0 per cent, respectively. The com- 
putations were made on the assumption that ground 
light was 10 per cent as intense as sky light. If the 
ground light were relatively greater, the obscura- 
tions percentages were smaller. In calculating the 
obscuration of the first two targets, the areas of the 
supporting poles, which were above the horizon rela- 
tive to the rocket trajectories, were considered part 
of the target. 

It was necessary that the fuzes pass under the 
target to receive a sufficient target signal. Attempts 
to use black targets on the ground were unsuccess- 
ful as the light change relative to the surrounding 
terrain was not sufficient to operate the fuze, except 
at very close passage. 



Figure 6. Large target consisting of pieces of black 
cloth attached to 15x75-ft fishnet for photoelectric 
rocket fuze tests. 


The launcher on the horizontal ranges was fixed 
in position. During the latter part of the develop- 
ment, a special tube launcher 45 ft long was used to 
reduce rocket dispersion. The terrain between the 
launcher and the target had to be level and uniform 
in color in order to avoid pretarget functions due to 
ground light variations. Visual and photographic 
observations from the launcher position and from a 
side station along a line at right angles to the trajec- 
tory at the target provided direct measurements of 
burst position. 

The differences and relative merits of high-angle 
and horizontal firing ranges were: 




CONFIDENTIAL 


RADIO REPORTER TESTS 


73 


1. Rate of fire. Testing was much more rapid on 
the horizontal range due to the fixed mounting of 
the target and launcher. High-angle targets had to 
be raised and lowered each day, and the launcher 
had to be aimed on each round because of drift of 
the target. 

2. Accuracy of observation. On horizontal ranges 
all coordinates of burst position and target passage 
distance were seen at right angles. Accurate data 
were obtained by direct measurement of photo- 
graphic films and were checked by visual observa- 
tions. In high-angle firing, the observations gen- 
erally had to be made at oblique angles. Burst posi- 
tions were obtained by trigonometric calculations 
based on film measurements and transit data. Grad- 
ual motion of the target made it necessary to make 
surveying measurements on each round. Small 
errors in these measurements resulted in an appre- 
ciable loss of accuracy in burst location determina- 
tions. Due to the oblique angle of view, direct visual 
observations were of little value. (See previous 
comment in text relative to Figure 5.) 

3. Flight range. The greater flight range in high- 
angle fire was an advantage since it provided infor- 
mation on rounds which did not function on the 
target. On fuzes which had the self-destruction fea- 
ture, the high-angle range provided a test of the 
reliability of self-destruction. On the horizontal 
range, the self-destruction score was of no signifi- 
cance, as late functions might have been due to 
either ground approach light variations or self- 
destruction; moreover, flight times overlapped the 
spread of self-destruction times. On fuzes which 
were not provided with self-destruction, the long 
time of flight on high-angle shots provided valuable 
engineering information concerning rounds which 
did not function on the target. 

4. Target signal. The high-angle target was free 
from disturbance by nearby objects. Target signals 
on horizontal ranges were sometimes affected by the 
poles which supported the target or by ground light 
variations. Some uncertainty in the interpretation 
of burst position data was thus introduced when 
horizontal ranges were used. 

5. Launcher. A long launcher to reduce dispersion 
could be used in horizontal fire since the launcher 
and target were fixed. A launcher of equal length 
would have been too cumbersome for high-angle 
fire since the launcher had to be aimed on each 
round. Small dispersion reduced the number of 


rounds necessary to determine the radius of action 
against small targets. 

6. Sun effect. Horizontal ranges, on which the 
direction of fire was approximately due north, were 
free of sunfiring effects throughout the day. In high- 
angle fire, the sun was at a critical angle at some 
time of day, no matter what direction of fire was 
used, unless the target or launcher location was 
changed when the sun angle became critical. 

To summarize, horizontal ranges were superior in 
most respects and ultimately replaced high-angle 
fire for all development and acceptance tests. How- 
ever, the spherical balloon used in high-angle firings 
was ideal for engineering purposes in evaluating 
fuze sensitivity and was not equaled by the small 
targets hung from poles. The technique for sensi- 
tivity testing with a single small target or series of 
targets was still under development when the work 
on photoelectric fuzes was stopped. 

Horizontal ranges were used for acceptance tests 
on production lots. 9 The primary purpose of these 
tests was to determine whether production samples 
would meet specified reliability requirements. Large 
targets were used, and the target signal was ordi- 
narily well above the fuze threshold. The sensitivity 
of production lots was controlled primarily by lab- 
oratory tests. 

75 RADIO REPORTER TESTS 

Radio reporters provided a means for determining 
behavior of the photoelectric fuze throughout the 














f 






S' 


A 




; 

T 

A / 



J 



(V 

A 



1 

/ 

/ 












v 

v\ 



















A 

















0 1 2 J 4 9 • 7 •• 10 II 12 14 19 16 17 19 19 20 


SCCONOS 

Figure 7. Photocell current versus time record ob- 
tained by use of radio reporter. 

flight of the projectile. The principal use of the 
reporters was for determination of the magnitude of 
posed new test ranges. 5 ’ 8 ’ 10 ’ 13 - 14 Reporters also pro- 



74 


FIELD TEST METHODS FOR PE FUZES 


posed new test ranges. 5 ' 8 ’ 10 ’ 13 ’ 14 Reporters also pro- 
vided engineering information on rate of yaw, sun 
pulses, and microphonics. 11 

A radio reporter consists primarily of a short- 
wave radio transmitter whose output is modulated 
by the output of the fuze. A receiver on the ground 
picks up the signals from the bomb or rocket which 
carries the fuze, and transfers them to an oscillo- 
scope, where they can be observed visually and re- 
corded photographically for detailed study. Some of 


the principles employed in the radiosonde , a widely 
used device for transmitting weather information 
from the upper atmosphere to the ground, were em- 
ployed in reporter design. 2 - 3 - 10 

A reporter record for a rocket fired from the 
ground is shown in Figure 7. Photocell current is 
plotted as a function of time. The ripples in the 
curve were apparently due to rocket yaw and the 
high peak to the sun. The curve marked T indicates 
the trajectory of the rocket. 


Chapter 8 


EVALUATION OF PE FUZES a 


81 SERVICE TESTS ON T-4 

T hree service tests were performed on T-4 fuzes. 

These were tests performed by the Ordnance 
Department to determine the suitability of the fuzes 
for specified operational uses. Other tests on PE 
fuzes reported in this chapter were development 
tests or routine acceptance tests. 

The service tests were: (1) 12 salvos, 5 rounds 
at 0.1 -second interval per salvo, 5-tube stationary 
launcher, HE-loaded M-8 rockets, Aberdeen, June 
23, 1943; 32 (2) 500 rounds, fired singly from a sta- 
tionary launcher, HE-loaded M-8 rockets, Aber- 
deen, May 1943; 50 * 51 (3) 24 rounds, fired singly 
from a stationary launcher, inert-loaded, S^-in. 
Cenco practice rockets, Fort Bragg, April 14, 15, 
1943. 9 > 26 

These tests were performed in preparation for a 
proposed use of the M-8 rocket with proximity fuzes 
as a barrage antipersonnel weapon by the Ground 
Forces. Tests (1) and (2) were the only tests of T-4 
fuzes on HE-loaded rockets. 

The Fort Bragg firings (3) were intended to test 
the ground approach firing characteristics of the 
T-4 fuze. The rounds were fired over various types 
of terrain. Twenty -two rounds, fired at angles of 
elevation of 15 to 30 degrees, functioned properly 
at heights visually estimated at 2 to 35 ft. Two 
rounds, fired at an angle of elevation of 65 degrees, 
functioned near the tops of the trajectories, prob- 
ably due to the sun. 

It should be noted that ground approach opera- 
tion of the T-4 fuze occurs on a probability basis. 
An adequate variation in reflected light from the 
ground has to be seen by the fuze in order for 
operation to occur. As indicated by the Fort Bragg 
tests, the probability that such a variation will be 
seen appears very high. The properties of the fuze 
as a ground approach weapon were investigated 
when it became evident that the weapon, because 
of high dispersion of the M-8 rocket, would not 
be used in the air-to-air role as originally in- 
tended. 

The 500 HE-loaded rounds, fired at Aberdeen, 

a This chapter was written by Alex Orden of the Ordnance 
Development Division of the National Bureau of Standards. 


were intended primarily as a test of the safety of 
the fuzes with respect to rearward fragments from 
early functions, possibility of functions before arm- 
ing, safety in handling, and any other safety prob- 
lem that might appear in the firing of a large num- 
ber of rounds. A few fragments from early functions 
flew back in the general direction of the launcher. 
This was not judged a serious safety hazard. There 
were no early functions before arming; hence the 
tests were considered to have proved the safety of 
the fuzes for general use. 

The purpose of the 5-round HE salvos at Aber- 
deen was to determine whether or not sympathetic 
firing occurred. By sympathetic firing is meant the 
functioning of one or more fuzes during flight, 
caused by the effects of functioning of another fuze 
during flight. There are several ways in which the 
functioning of one fuze may cause others to function 
sympathetically. These may be grouped as follows: 
(1) on seeing the smoke, flame or fragments from 
a preceding HE burst, (2) microphonic disturbances 
set up either by the striking of the rocket by a frag- 
ment from another burst or by sound shock. 

The launcher had 5 tubes about 10 ft long, 
mounted in parallel on a wooden frame with about 
10 in. between centers. The firing elevation was 50 
degrees. To induce sympathetic action during the 
useful portion of the flight, one fuze in each salvo 
was set to fire intentionally at approximately 2.5 
sec after ignition. 

The rockets in each salvo were fired at intervals 
of nominally 0.1 sec. On account of variable lag 
in ignition of the propellant, the interval between 
take-off of successive rockets was irregular, and in 
some instances a rocket actually preceded one which 
it was supposed to follow. Rocket velocities were 
about 1,000 ft per sec. 

The results are shown in Figure 1. The length of 
the time bars gives a rough measure of the probable 
error in the time measurements. Figures in paren- 
theses (immediately following the salvo number) 
give the order of firing of the rocket with the inten- 
tional burst fuze. A zero indicates that this round 
did not burst. Numbers in brackets (at extreme 
right) give the number of rockets which failed to 
fire in the salvo. All rounds were expected to burst 


75 


CONFIDENTIAL 




76 


EVALUATION OF PE FUZES 


by self-destruction if they were not accidental ear- 
lies or sympathetic functions. 

On the basis of the results shown in the figure, it 
appeared that T-4 fuzes on M-8 rockets were quite 
susceptible to sympathetic functioning. The effect 
could be reduced by increasing the salvo time inter- 
val. However, under normal conditions, without in- 



TIME TO BURST BY STOPWATCH (SEC) 


Figure 1. Function times on salvos of five T-4 fuzes 
fired at 0.1-second intervals on M-8 rockets to test for 
sympathetic functioning. 

tentional self-bursts, sympathetic functioning would 
probably not be a serious problem as the percentage 
of accidental early functions of T-4 fuzes was gen- 
erally low. Sympathetic bursts caused by functions 
on a target would probably detract little from the 
effectiveness of the fuze. 

8.2 T-4 FUZES FIRED FROM A 

FIGHTER AIRPLANE 

One hundred and seventy-six T-4 fuzes were fired 
from a U. S. Army P-40 fighter plane. These tests 
were conducted at Aberdeen Proving Ground, Sep- 
tember 29, 1942, through January 24, 1943. The 
fighter plane had 3 launcher tubes mounted in a 
cluster under each wing, permitting 6 rounds to be 
carried per mission (see Figure 2, Chapter 7). The 
projectiles were fired singly. The fuzes were T-4 
experimental pilot production samples. 

The target range was over the Chesapeake Bay 
at Mulberry Point. The projectiles were fired 
southward at target balloons tethered above the bay. 
The target was at first tethered from the shore, but 
in view of the high percentage of boundary func- 


tions caused by shoreline irregularities it was moved 
out over the bay. b 

The target consisted of 1 to 4 sausage-shaped, 
black balloons (Figure 1, Chapter 7), or a 12-ft 
spherical balloon (Figure 3, Chapter 7). The targets 
were tethered over the bay at altitudes of 150 to 
500 ft. 

Difficulties in the firing technique caused erratic 
results in the first 8 rounds fired. These are excluded 
in the following overall summary: 


Function on target 54 

Early function 9 

Function beyond target or 
self-destruction 39 

No function 66 

Total 168 rounds 


The above figures give a gross score for the fuzes 
of 54/168 = 32 per cent. The gross score of 32 per 
cent functions on target represents the performance 
of the fuze-rocket combination. No reliability score 
for the fuzes alone can be given since reasonably 
accurate trajectory data are available for only a 
small percentage of the rounds fired. The available 
trajectory data plus visual observations indicated 
that, within a radius of 50 to 75 ft from the target, 
the fuze was highly reliable. The large number of 
nonfunctions apparently represent rounds on which 
the flights were too short for self-destruction. The 
fuzes generally did not burst on approach to water, 
an expected result because of the uniform reflection 
from the water’s surface. 

Figure 2 shows the distribution of function time 
of the rounds that functioned on the target. The 
mean time was 1.6 sec. Assuming a rocket velocity 
relative to the plane of 800 ft per sec and a plane 
velocity of 340 ft per sec (230 mph), the average 
firing range was consequently about 1,800 ft. 

8-3 ACCEPTANCE TESTS OF MC-380 FUZES 

Acceptance tests were made on production lots of 
PE fuzes produced by four manufacturers. The tests 
were conducted at Fort Fisher Proving Ground, 
North Carolina; Blossom Point Proving Ground, 
Maryland; and Aberdeen Proving Ground, Mary- 
land. 

The Fort Fisher Proving Ground N range was 
laid out so that the projectile flight was over uni- 

b Random functioning of the fuzes due to ground light 
variation was a difficulty expected in testing. At the higher 
altitudes anticipated in operational use, random ground light 
variations would have a negligible effect. 


CONFIDENTIAL 


- 


SMALL-TARGET TESTS WITH T-4 


77 


form brownish-green marsh grass. The launcher and 
fish-net target are described in Chapter 7. The target 
rested in a horizontal plane at 75 to 85 ft above the 
ground, with its long dimension normal to the trajec- 
tory of the projectile and its center 1,000 ft from 
the breech of the projector. 



Figure 2. Times of function on target of T-4 fuzes 
on M-8 rockets fired from P-40 airplane at Aberdeen 
Proving Ground. 

The PE target range at Blossom Point Proving 
Ground was quite similar. Projectors were, at first, 
a 12-ft seamless steel tube, and, later, a 45-ft tube, 
made up in three sections. The range was 1,240 ft 
for the 12-ft tube and 1,100 ft for the 45-ft tube. 
The target was supported 95 to 105 ft above the 
ground and consisted of a fish net, 15x75 ft in size, 
to which were attached pieces of black cloth, 3 ft 
square. The whole target was fireproofed. 

The PE range at Aberdeen Proving Ground was 
located at C Field. The firing was done from a 40-ft 
seamless steel tube of 4% in. inside diameter, located 
on a tower approximately 60 ft in height. The tower 
was located very close to the water’s edge. The tar- 
get was located 1,000 ft from the tower and sup- 
ported by four poles placed in the water. The 


trajectory was over water, except for the first few 
feet. Therefore, firing was done over a uniform sur- 
face up to the target. The target consisted of screen 
wire 10x65 ft, which supported dark painted canvas 
at 70 ft above the water level. 

The projectile used for acceptance firing of the 
fuzes was the Army M-9 practice 4.5-in. rocket. 

The fuze assembly consisted of the T-4 fuze nose, 
a BA-55 battery and a SW-200 (0.4-sec or 0.7- 
sec) switch, assembled and inserted in an M-381 
booster housing (see Figure 2, Chapter 3) . The com- 
ponents MC-380, BA-55, and SW-200 were checked 
on the Army Field Test Set IE-28 for safety and 
proper operation before final assembly. The booster 
housing contained a black powder wafer spotting 
element to indicate the functioning of the fuze. 

The acceptance test was normally performed on a 
sample of 20 units from each production lot of 1,000 
fuzes. All samples were selected at random from the 
lot after the fuzes in the lot had successfully passed 
all other requirements of the specification. In all 
cases the projectile was aimed to pass under the tar- 
get. The region of sensitivity for the target was 
generally defined as the region beneath the target, 
at least 30 ft above the ground and between the 
poles supporting the target. 

Normally a production lot of 1,000 fuzes was ac- 
cepted when 10 fuzes out of the sample of 20 had 
functioned within the region of sensitivity of the 
target. If more than 10 of the 20 samples failed to 
function properly, further tests were conducted, as 
specified by the contracting officer. 

Table 1 is a summary of the acceptance tests on 
fuzes produced by each manufacturer. Only fuzes 
passing within the region of sensitivity are included 
in the scoring. 

84 SMALL-TARGET TESTS WITH T-4 
8,4,1 Introduction 

Target tests with the T-4 fuze may be divided into 
two classes: (1) small targets, which tested the sen- 
sitivity of the fuze as well as its reliability, and (2) 
large targets, which provided pulses well above the 
threshold, and hence served only as a test of fuze 
reliability. Early tests on preproduction samples of 
the T-4 fuze at Fort Fisher against a 12-ft diameter 
balloon were small-target tests. Later the technique 
of testing against a large target (hung from poles) 
was developed for acceptance testing. Reliability 


confid: 


78 


EVALUATION OF PE FUZES 


Table 1. A. Acceptance test results: Westinghouse Electric and Manufacturing Co. 


Lot 

numbers 

No. counted 
in score 

On target * 

Early * 

Late or 

self-destruction * 

Nonfunction * 

1-128 

1,446 

1.281 

87 

14 

64 

(88.6%) 

(6%) 

(1%) 

(4.4%) 

1-10 

153 

142 

3 

0 

8 



(92.8%) 

(2%) 


(5.2%) 

11-20 

121 

116 

3 

0 

2 



(95.9%) 

(2.4%) 


(1.7%) 

21-30 

109 

101 

5 

0 

3 



(92.7%) 

(4.6%) 


(2.7%) 

31-40 

148 

139 

5 

1 

3 



(93.9%) 

(3.4%) 

(0.7%) 

(2%) 

41-50 

105 

95 

4 

0 

6 



(90.5%) 

(3.8%) 


(5.7%) 

51-60 

100 

92 

3 

0 

5 



(92%) 

(3%) 


(5%) 

61-70 

100 

83 

11 

0 

6 



(83%) 

(11%) 


(6%) 

71-80 

130 

104 

17 

0 

9 



(80%) 

(13%) 


(7%) 

81-90 

100 

84 

12 

1 

3 



(84%) 

(12%) 

(1%) 

(3%) 

91-100 

100 

82 

12 

1 

5 



(82%) 

(12%) 

(1%) 

(5%) 

101-110 

100 

88 

4 

3 

5 



(88%) 

(4%) 

(3%) 

(5%) 

111-120 

100 

91 

3 

3 

3 



(91%) 

(3%) 

(3%) 

(3%) 

121-128 

80 

64 

5 

5 

6 



(80%) 

(6.25%) 

(6.25%) 

(7.5%) 

* Figures in 

parentheses indicate percentages of the total. 





Table 1 

. B . Acceptance test results: Western Electric Co. 


Lots 

No. counted 
in score 

On target * 

Early * 

Late or 

self-destruction * 

Nonfunction * 

1-103 

1,063 

967 

35 

15 

46 


(91%) 

(3.3%) 

(1.4%) 

(4.3%) 

1-10 

120 

109 

7 

2 

2 



(90.8%) 

(5.8%) 

(1.7%) 

(1.7%) 

11-20 

113 

100 

10 

0 

3 



(88.5%) 

(8.8%) 


(2.7%) 

21-30 

100 

92 

1 

0 

7 



(92%) 

(1%) 


(7%) 

31-40 

100 

91 

2 

0 

7 



(91%) 

(2%) 


(7%) 

41-50 

100 

91 

3 

0 

6 



(91%) 

(3%) 


(6%) 

51-60 

100 

94 

2 

0 

4 



(94%) 

(2%) 


(4%) 

61-70 

100 

93 

1 

3 

3 



(93%) 

(1%) 

(3%) 

(3%) 

71-80 

100 

90 

1 

6 

3 



(90%) 

(1%) 

(6%) 

(3%) 

81-90 

100 

90 

1 

2 

7 



(90%) 

(1%) 

(2%) 

(7%) 

91-103 

130 

117 

7 

2 

4 



(90%) 

(5.4%) 

(1.5%) 

(3.1%) 


* Figures in parentheses indicate percentages of the total. 


CONFIDENTIA 


SMALL-TARGET TESTS WITH T-4 79 


Table 1. C. Acceptance test results: Philco Corporation. 

Lots 

No. counted 
in score 

On target * 

Early * 

Late or 

self-destruction * 

Nonfunction * 

1-62 

640 

580 

24 

1 

35 



(90.6%) 

(3.7%) 

(0.2%) 

(5.5%) 

1-10 

121 

103 

14 

0 

4 



(85.1%) 

(11.6%) 


(3.3%) 

11-20 

99 

96 

0 

0 

3 



(97%) 



(3%) 

21-30 

100 

87 

4 

0 

9 



(87%) 

(4%) 


(9%) 

31-40 

100 

96 

2 

0 

2 



(96%) 

(2%) 


(2%) 

41-50 

100 

89 

2 

0 

9 



(89%) 

(2%) 


(9%) 

51-62 

120 

109 

2 

1 

8 



(90.8%) 

(1.7%) 

(0.8%) 

(6.7%) 

* Figures in parentheses indicate percentages of the total. 


Table 1. D. Acceptance test results: Wurlitzer Co. 

Lots 

No. counted 
in score 

On target * 

Early * 

Late or 

self-destruction * 

Nonfunction * 

1-99 

1,043 

935 

58 

8 

42 



(89.6%) 

(5.6%) 

(0.8%) 

(4%) 

1-10 

143 

127 

9 

2 

5 



(88.8%) 

(6.3%) 

(1.4%) 

(3.5%) 

11-20 

107 

100 

5 

0 

2 



(93.5%) 

(4.7%) 


(1.8%) 

21-30 

114 

107 

6 

1 

0 



(93.9%) 

(5.2%) 

(0.9%) 


31-40 

108 

99 

7 

1 

1 



(91.7%) 

(6.5%) 

(0.9%) 

(0.9%) 

41-50 

100 

90 

8 

0 

2 



(90%) 

(8%) 


(2%) 

51-60 

100 

89 

6 

0 

5 



(89%) 

(6%) 


(5%) 

61-70 

106 

89 

6 

1 

10 



(84%) 

(5.7%) 

(0.9%) 

(9.4%) 

71-80 

100 

90 

4 

1 

5 



(90%) 

(4%) 

0%) 

(5%) 

81-90 

100 

92 

5 

1 

2 



(92%) 

(5%) 

(1%) 

(2%) 

91-99 

90 

76 

3 

1 

10 



(84.5%) 

(3.3%) 

(1.1%) 

(11.1%) 


* Figures in parentheses indicate percentages of the total. 


tests against a large target were adequate for the 
occasional experimental tests required as well as for 
acceptance tests. Late in the production program, 
attention was directed toward circuit revisions and 
relaxation of component specifications (see Sec- 
tion 8.6 of this chapter) . In order to test the sensi- 
tivity of fuzes built to less rigid specifications, the 
large targets hung from poles were replaced by 


small panel targets as described in Chapter 7 of this 
volume. 

This section presents the results of tests against 
small targets in order to summarize the available 
field-test information on fuze sensitivity. The fol- 
lowing data are available: (1) About 300 rounds of 
preproduction T-4 fuzes were fired against the 12-ft 
diameter balloon at the Laboratory Range at Fort 


CONFIDENTIAL 


80 


EVALUATION OF PE FUZES 


Fisher. (2) About 250 T-4 fuzes (some standard 
units, some with modified circuits, and some with 
components outside specifications) were tested on 
the North Range at Fort Fisher against a triplanar 
black panel assembly. Each of the three intersecting 
planes of the target was 4x4 ft. The target was hung 
from a rope between the two front poles on the 
range. 13 (3) About 200 T-4 fuzes (standard and 


8 - 4 - 2 Preproduction Tests at 

Fort Fisher 

The test conditions in high-angle firing on the 
Laboratory Range at Fort Fisher have been de- 
scribed in Chapter 7. The results of the firings 
against the 12-ft diameter balloon are shown in 
Figure 3. In the construction of the diagram, the 



Figure 3. Distribution of type of operation with passage distance. T-4 fuzes on ZV^-in. practice rockets fired against 
12-ft diameter black balloon. T — target function; SD — self-destruction; L — late function; NF — no function. 


with modifications) were fired at Blossom Point 
against a four-target array which gave a series of 
pulses of increasing magnitude (see Section 7.4) . (4) 
During the acceptance tests against a large target, 
analysis of burst positions demonstrated that a large 
number of fuzes were triggered by front poles, used 
to suspend the targets, before seeing the intended 
target. Calculations showed that the pulse from the 
poles was of proper size to provide a marginal test 
of fuze sensitivity. 29 

The rounds fired from a plane against sausage 
balloons (Section 8.2) were small-target tests, but 
the data obtained on burst positions and passage 
distances were too inaccurate to use as a measure 
of the radius of action [ROA]. 


distances of passage on the rounds fired were ar- 
ranged in the order of increasing distance of passage 
from the target and counted off in successive groups 
of 20 rounds. The figure shows the distribution 
among target functions, late random functions 
(functions beyond the target and too early for self- 
destruction), self-destruction functions, and non- 
functions in each of the groups of 20. There were 41 
early functions. The distances of passage from the 
target of the early functions were not included in the 
counts for Figure 3. 

The figure shows that the percentage of functions 
on target remained constant, within expected statis- 
tical fluctuations, up to a radius of passage of ap- 
proximately 60 ft. With increasing passage distance, 



SMALL-TARGET TESTS WITH T-4 


81 


the percentage of functions on targets then de- 
creased, while the percentage of self-destruction 
functions increased. 

8,4,3 Tests against Small Target Hung 
from Poles on the North Range 
at Fort Fisher 

Tests were made against the triplanar 4x4-ft tar- 
get on the North Range at Fort Fisher to obtain a 
field check of sensitivity on fuzes modified in vari- 
ous minor ways. The fuze changes and effects on 
performance are reported in Section 8.6 of this chap- 
ter. This section deals only with the radius of action 
against the small target. 

The majority of the various modifications of the 
T-4 fuzes had shown characteristics practically 
identical with the standard units in laboratory tests 
and, likewise, gave about equal field performance. 
However, several of the modified types showed sen- 
sitivity somewhat inferior to the standard model. 
The results are summarized in Table 2. The rounds 
not accounted for as functions on poles, on the tar- 
get, late or by self-destruction were earlies, rocket- 
motor failures, or duds. Pole functions are consid- 
ered proper functions. They represent rounds more 
sensitive than average. 

Except for the third line of the table, the per- 
centage of rounds which passed the target and 


functioned later is too small to obtain a measure of 
the radius of action against the 4x4-ft target. The 
results merely show that for the standard fuze and 
for the modified fuze (whose performance was ap- 
proximately the same as the standard model, lines 
2, 4, 5 of the table), the fuze provided high target 
scores up to a radius of passage of at least 35 ft. The 
number of functions on poles was greater on the 
standard model (lines 1 and 5) than on the modified 
models which gave equally good performance (lines 2 
and 4) ; hence the standard model was apparently a 
little more sensitive. 

The lower sensitivity of the group with substand- 
ard pentodes had been expected on the basis of 
laboratory characteristics. A study was made of 
round by round correlation of laboratory sensitivity 
data with field results for this group. (The labora- 
tory methods of measuring sensitivity are described 
in Chapter 6.) 

Since the laboratory threshold was measured with 
a continuous alternating signal and the light pulse 
in the field was a single pulse, the frequency re- 
sponse of the fuze must be taken into account in 
correlating the laboratory and field results. Direct 
correlation is expected for groups of fuzes with the 
same frequency response. The fuzes with substand- 
ard pentodes consisted of groups with pentodes made 
by three manufacturers: Sylvania, Raytheon, and 
Hytron. Those with Raytheon and Hytron pentodes 


Table 2. Sensitivity against 4x4-ft target. 


Date of 
test 

Type 

No. 

fired 

Per cent 
proper 
(on target 
or poles) 

No. 

func- 

tioned 

on 

poles 

No. 

func- 

tioned 

on 

target 

Target 

passage 

distance 

of 

function 

on 

target 

(ft) 

No. of 
late 
func- 
tions and 
self- 

destruction 

Target 
passage 
distances 
of late 
functions 
and self- 
destruction 
(ft) 

May 30, 1943 

Standard model 

30 

83 

6 

19 

24-35 

2 

27-33 

May 30, 1943 

New high sensitivity photo- 
cells and reduced input 
resistor (2 to 10 meg) 

62 

87 

2 

52 

22-32 

4 

27-36 

May 30, 1943 

Substandard pentodes and 
increased amplifier out- 
put circuit resistors 

59 

64 

1 

37 

20-30 

18 

25-38 

June 10, 1943 

RPEB-2 (see Section 8.6) 

48 

83 

0 

40 

28-40 

0 


June 17, 1943 

Standard model with photo- 
cells outside specifications 

39 

87 

15 

19 

15-37 

1 

27 


CONFIDENTIAL 



82 


EVALUATION OF PE FUZES 


had the average frequency response for T-4 fuzes 
and hence may be considered together in relating 
laboratory to field results. Those with Sylvania pen- 
todes are considered separately since they had am- 
plifiers which were peaked at a frequency of about 
200 instead of the standard at about 100 c. 

The correlation between laboratory and field re- 
sults is shown in Figure 4. The radius of action of a 




Figure 4. Correlation of laboratory and field test re- 
sults for T-4 fuzes with substandard pentodes. Rounds 
fired against 4x4-ft target. Top figures for units with 
Raytheon and Sylvania pentodes. Bottom figure for 
units with Sylvania pentodes. 

fuze is expected to be inversely proportional to the 
laboratory threshold, T. The magnitude of the tar- 
get signal is assumed to vary inversely as the square 
of the distance of passage, r 2 . Therefore, the per- 
centage of functions on target is expected to decrease 
as the product, r 2 T, increases, while the percentage 
of rounds which fail to function on the target in- 
creases. Only late functions and self-destructions 
are counted as failures to function on the target for 
the purpose of this correlation, since duds were 


probably dead fuzes, at the time they passed the 
target. The target curve in Figure 4 gives the per- 
centage of fuzes which functioned on the target for 
all r 2 T values greater than the value for a given 
point. The late curve gives the percentage which 
functioned late or by self-destruction for all smaller 
values of r^T. 

If there were no correlation between laboratory 
and field data, both the target and late curves would 
be horizontal lines at 50 per cent. If there were per- 
fect correlation, the two curves would fall to zero 
at the same point on the abscissa scale. Thus Fig- 
ure 4 indicates considerable correlation. The per- 
centage value at the point of intersection may be 
taken as the percentage error in correlation. 

Some factors which account for errors in corre- 
lation are: 

1. The magnitude and shape of the target signal 
would vary somewhat from round to round at con- 
stant radius of passage due to variations in pro- 
jected area of the target with position of the trajec- 
tory relative to the target. 

2. There is some radial asymmetry of fuze 
sensitivity; hence the radius of action would vary 
as the rocket rotates in flight. The threshold is 
measured at a particular radial angle which is gen- 
erally not the same as the angle at which the fuze 
sees the target. 

3. There is some variation of frequency response 
among individual fuzes of a given type; therefore, 
there is variation of the ratio of 60-c threshold to 
target sensitivity. 

4. Microphonics and ground light variations are a 
variable percentage of the required firing signal. 
Round-by-round variation of rocket vibration varies 
the microphonics level. Ground light variations may 
change continually with sun position and cloud con- 
ditions. 


«. 4.4 Tests against Series of Targets 
at Blossom Point 

The four-target array has been described in 
Chapter 7. Two tests with standard and modified 
fuzes were made against this target, but in only one 
were trajectory conditions adjusted properly to give 
a measure of fuze sensitivity. 38 

The results of this test are in Table 3. The modi- 
fied fuzes (designated RPEB-2) are divided into 
four groups according to the type of pentode in the 


COT 


CONFIDENTIAL 


SMALL-TARGET TESTS WITH T-4 


83 


Table 3. Results of field tests against series of four targets at Blossom Point, October 2, 1943* 

Units 

No. 

fired 

Proper 

function 

Early 

Dud 

Score 

No. on 
target 

12 3 4 

Average 
thresholds 
at normal 
light level 

RPEB-2 Hytron pentode 

20 

19 

0 

1 

95% 

0 1 16 2 

0.98 

RPEB-2 Raytheon pentode 

19 

18 

0 

1 

95% 

0 3 14 1 

1.06 

RPEB-2 Sylvania pentode 

20 

17 

2 

1 

85% 

0 3 10 4 

0.85 

RPEB-2 GE pentode 

20 

16 

4 

0 

80% 

2 5 9 0 

0.54 

MC-380 Hytron pentode 

30 

30 

0 

0 

100% 

0 0 26 4 

0.92 


^Target 1 : 3x4 ft at approximately 75- ft radius. Target 3: 3x5 ft at approximately 30-ft radius. 

Target 2: 4x11 ft at approximately 75- ft radius. Target 4: 3x10 ft at approximately 30-ft radius. 


amplifier. The differences between target distribu- 
tion among the four targets indicate that the four- 
target array successfully distinguished differences 
in sensitivity by type of fuze. Units with General 
Electric [GE] pentodes were most sensitive; almost 
half were triggered by the first two targets. A fur- 
ther indication that this was the most sensitive 
group is given by the fact that it had the highest 
percentage of early functions. The standard T-4 
fuzes were least sensitive. 

The units with GE pentodes were also shown most 
sensitive by laboratory threshold measurements 
(60-c test). Differences in average threshold were 
less pronounced and did not correlate directly with 
the relative sensitivities indicated by the target 
array. Better correlation would probably have been 
established had variations in target passage dis- 
tance been taken into account. 

On the tests with the standard T-4 fuzes, the 26 
rounds which functioned on the third target (3x5 ft) 
passed that target at radii ranging from 25 to 50 ft. 
None of the standard fuzes functioned on the second 
target, which provided a peak obscuration of about 
1.8 per cent. The peak obscurations by the third 
target for the range of passage distances 25 to 50 ft 
were approximately 4 to 2 per cent respectively. 
Thus the minimum pulse on which any fuze oper- 
ated was about 2 per cent. A few which failed to 
function on the fourth target passed the third at 
distances of 35 to 40 ft, indicating that occasional 
fuzes may fail to function on pulses of about 3 per 
cent. It has been shown (see Chapter 4) that the 
threshold for field pulse targets is generally 2 to 3 
times greater than the laboratory threshold meas- 
ured at 60-c, continuous, alternating light signal. 


The 60-c threshold of T-4 fuzes averages about 1 
per cent. Thus the results against the four-target 
array are in general agreement with expectations. 

Functions on Poles during 
Acceptance Tests 

Analysis of the burst position data of about 300 
rounds of production T-4 fuzes, fired in acceptance 
tests on the North Range at Fort Fisher, showed 
that 64 per cent of the proper functions had fired 
against the front poles rather than against the large 
cloth piece target. A typical plot of the locations of 
the bursts for one lot acceptance test is shown in 
Figure 5. The view of the burst positions from above 
shows 8 bursts lying in a cluster approximately 25 
degrees ahead of the poles. Obviously, these units 
functioned against the poles before they saw the 
cloth target. Similarly, the side view shows that two 
units passed the poles and functioned against the 
cloth target. 

The pulse from the poles is due largely to the part 
of the poles above the horizon, relative to the rocket 
trajectory; therefore, the magnitude of the pole sig- 
nal decreases with increasing height of the trajectory 
above the ground. The distribution of functions be- 
tween poles and cloth target for about 300 rounds is 
shown in Figure 6. Up to 40 ft from the ground, 
approximately 90 per cent functioned on poles. It 
may also be seen that as the trajectory height in- 
creased the proportion of pole functions decreased 
to zero at 65 ft or higher. 

The amplitude of the obscuration pulse as a func- 
tion of trajectory height is shown on the right side 


84 


EVALUATION OF PE FUZES 


of Figure 6. The curves were obtained by computa- 
tion. Maximum pole signals were obtained on rounds 
which passed exactly midway between the poles and 
saw both poles simultaneously. Minimum signals 
were obtained when the trajectories were sufficiently 


than the thresholds measured at 60 c in the labora- 
tory (see Chapter 4). Thus the pole function firing 
signals of 1.5 to 3 per cent are in reasonable agree- 
ment with the average 60-c threshold of about 1 per 
cent. 



8 5 SUNFIRING TESTS ON T-4 FUZES 

The susceptibility of the T-4 fuze to firing on 
seeing the sun was known from the beginning of the 
development. However, no experiments were con- 
ducted on sun angle limits until the fuze was well 
along in production and consideration was being 
given to the development of improved models. Field 
tests in which the fuzes were intentionally fired to 
see the sun are summarized in this section. 19 ’ 36 


OIRECTION 

or ruoHT 


CLOTH 

TARGET 



SIDE VIEW 


Figure 5. Top and side view of burst positions on 
rounds fired in lot acceptance test at Fort Fisher 
Proving Ground. Small circles indicate positions of 
bursts. Scale: 1 mm per ft. 


off center laterally to receive distinct successive 
signals from the two poles. The curves for the right 
pole and left pole are the per cent signal for the 
separate poles on rounds which passed midway be- 
tween the poles. Actually, on off-center rounds on 
which the fuze would see the poles separately, the 
signal from the near pole would be larger, and from 
the far pole smaller. The lateral dispersion was 
small enough so that the signals from the two poles 
probably overlapped, at least in part, on most 
rounds; hence the firing signals were generally be- 
tween the both pole curve and the one pole curve. 
In the threshold zone for pole functions, 40 to 65 ft 
above the ground, the pulse amplitudes were in the 
range of 1.5 to 3 per cent. 

Pole pulses reached their peak amplitudes about 8 
milliseconds after the obscurations started. For this 
pulse time, the thresholds are 2 to 3 times greater 



Figure 6. Per cent of light obscuration and per cent 
of fuzes which functioned on “seeing” poles which 
supported target as function of height of rocket tra- 
jectory above ground in region of target. 


The aims of the tests were: (1) to determine the 
sunfiring properties of the fuze, (2) to obtain data 
for use in the development of the nonsunfiring fuzes. 
The tests involved the firing of 145 rounds “through 
the sun.” One hundred rockets were fired at such an 
angle of elevation that they would ride several 
seconds before the sun came into the field of view. 
Forty-five rounds were fired to see the sun imme- 
diately at arming. Observations of time of function 
and ballistic calculations to determine the direction 


CONFIDENTIAL 


REVISIONS OF T-4 CIRCUIT AND OF LABORATORY TEST REQUIREMENTS 


85 


of flight at the time of function permitted deter- 
mination of the sun angle (angle between the sun 
and the center of the field of view of the fuze) at 
the time of function. Use of a 44-ft long projector 
limited initial angular dispersion of the rockets and 
hence permitted reasonably accurate knowledge of 
the trajectories. 

The probability of sunfiring as a function of sun 
angle, based on the tests, is shown in Figure 7. The 





N 


















\ 


















\ 


















\ 

















fS 

V 

















\ 

V 





































s 









































12 3 4 3 6 7 8 9 10 II 12 13 14 IS 16 

ANGLE BETWEEN CENTER OF LENS ANO SUN 


Figure 7. Probability of sunfiring versus angle be- 
tween sun and center of field of view of fuze. 


maximum sun angle at which sunfiring occurred was 
16 degrees. The curve is based on the 100 rounds 
fired to pass into the sun sometime during the flight. 
There were 7 duds in the 100 rounds, but, since 
there was no means of determining whether these 
fuzes were alive after riding through the sun, these 
rounds were discarded. Seven duds per hundred is 
higher than average for this type of fuze; thus it is 
possible that the maximum probability in Figure 7 
should be about 0.97 rather than 1.0. However, this 
difference is negligible for practical purposes. 

The 100 rounds discussed above were fired with 
fuzes from which the self-destruction feature was 
removed. The 45 rounds which were fired to see the 
sun immediately at arming had fuzes with the self- 
destruction feature. The results were 

4 self-destruction; 

32 functions on arming (at about 0.75 sec) ; 

8 functions at 0.3 to 1.5 sec after arming; 

1 nonfunction. 

On the basis of these tests, it is clear that the T-4 
fuze cannot be used for ground-to-ground firing, 
except at very restricted azimuths. (See Section 8.7.2 
concerning tests on sunproofed modifications of the 
T-4 fuze.) For plane-to-plane application, the use 


of the fuze is feasible since the change in direction 
of flight during the useful target range is small. 
Computations on the basis of Figure 7 have shown 
that an average probability of sunfiring for random 
orientation of an initially horizontal trajectory in 
plane-to-plane firing is 0.14. This probability varies 
somewhat with season, time of day, geodetic lati- 
tude, and average firing range, but it is in no case 
large enough to preclude use of the fuze. The prob- 
ability can be reduced to zero by firing when flying 
in such directions that the fuze will not see the 
sun. 39 

86 REVISIONS OF T-4 CIRCUIT AND OF 
LABORATORY TEST REQUIREMENTS 

8,61 Revised Circuit 

Considerable engineering was done on the T-4 
fuze after basic specifications had been established 
and production started. This section summarizes 
field tests, intended to evaluate various proposed 
changes from the original standard design and speci- 
fications. The main object of the work was to relax 
certain requirements to facilitate production. 

In general, it was found that: 

1. As long as the amplifier-gain characteristics 
remained approximately the same, field scores were 
unimpaired. In particular, increased gain at lower 
frequencies increased the number of random func- 
tions. 

2. Increased amplifier gain obtained with more 
sensitive pentodes increased the number of early 
functions. This result indicated that the gain in the 
standard fuze was approximately optimum for re- 
liable performance. (See references 7, 8, 10, 11, 12, 
13, 15, 28, 37.) 

A revised circuit designated as RPEB-2 (Rocket, 
PE, Battery, second model) yielded scores compar- 
able with those obtained with standard T-4 fuzes. 
It was not expected that the revised circuit would 
improve performance under standard conditions, but 
rather that the circuit would be easier to build and 
also give as good or better performance than the 
previous model, under conditions of long storage. 

The circuit included a photocell of greater sensi- 
tivity (designated 1P24) and accordingly allowed 
the use of lower input impedances for the amplifier. 
This, in turn, permitted the use of pentodes with 
lower input impedance and reduced the requirement 
that the pentode maintain a high input impedance 


CONFIDENTIAL 


86 


EVALUATION OF PE FUZES 


over extended periods, i.e., remain “gas free.” (See 
references 14, 31, 33, 38.) 

8 62 Evaluation of Laboratory 

Microphonic Test 

Approximately 50 T-4 fuzes which failed the lab- 
oratory test for microphonics were fired in compari- 
son with standard fuzes. There was no correlation 
between the magnitude of the microphonics in the 
laboratory test and the incidence of early function. 
On the basis of this test, the microphonics test ap- 
peared to be inadequate. 16 ' 17 * 41 

8 7 TESTS ON EXPERIMENTAL MODEL 
ROCKET FUZES 

This section summarizes the field test results on 
models of photoelectric fuzes which did not go into 
factory production. The condenser model, zero stage 
model, and sunblocking model were under develop- 
ment at the time development work on photoelectric 
fuzes was stopped. Other improved models (double 
photocell, generator-powered, etc.) were under de- 
velopment in the laboratory, but had not reached 
the stage for field tests. Field tests on T-4 type fuzes 
with multistage amplifiers and on rocket fuze types 
which preceded the T-4 are summarized. 

8,71 Condenser-Powered Fuzes 45 ' 49 

The condenser-powered fuze, described in Chap- 
ter 5, has the advantage that it requires no B bat- 
tery. However, an external battery is required to 
charge the storage capacitor in the fuze just before 
the rocket is launched. 

One hundred condenser-powered fuzes were con- 
structed of which 31 were fired in field tests. 5 - 6 ' 23 
The results were: 29 target functions (93.5 per 
cent) ; 2 early functions. 

8 ' 7 ' 2 Sunproofed Fuzes 

The development work on fuzes which would 
allow the sun to pass through the field of view with- 
out firing had two phases: (1) simple circuit modi- 
fications of the T-4 fuze, (2) basic changes, such as 
use of the two photocells and double lenses (see 
Chapter 5). 

Sunproof modifications of the T-4 were developed 


and field tested. Basic new types were under devel- 
opment in the laboratory, but did not reach the stage 
of field testing. 

During the period of major work on the sunproof 
models, interest in rocket proximity fuzes was di- 
rected toward the ground-to-ground (rocket bar- 
rage) application. While the PE fuze was suitable 
for air-to-air use in spite of sunfiring (see Sec- 
tion 8.5), this defect made it entirely unsuitable for 
ground-to-ground firing, since in this use the fuze 
would see the sun at some point in its trajectory 
under most firing conditions. 

The development of a sunproof fuze for the 
ground-to-ground application was simpler than for 
air-to-air use for two reasons: 

1. The ground-to-ground fuze could be designed 
to become inoperative when it saw the sun and to 
revive when the sun passed out of the field of view. 
This required a simpler design than for a fuze which 
would operate properly even with the sun in view. 
For air-to-air use, the latter more difficult design 
would have been required. 

2. The light levels encountered on approach to 
ground are considerably lower than at high altitudes. 
This simplified the problem of blocking the effect 
of the very high light level of direct sunlight. 

The tests, described below, on sunproof modifica- 
tions of the T-4 fuze showed successful elimination 
of sunfiring. However, these tests also showed that 
the basic design of the T-4 fuze is not satisfactory 
for ground approach use, since, under some terrain 
conditions and angles of approach, the light varia- 
tion seen by the fuze is so small as to result in duds 
or very low burst heights. Several tests were carried 
out in an attempt to find a target which would trig- 
ger the fuzes on approach to ground. No really satis- 
factory target was found, as shown in the results 
summarized in Table 4. The ranges were selected so 
that in each case there would be some period during 
the day when the fuze would not see the sun on any 
part of the trajectory. This permitted evaluation of 
the effect of the sunproofing feature on normal per- 
formance. 

These results indicated that the T-4 could be 
successfully modified to be sunproof with no loss in 
ground approach performance, but that ground ap- 
proach triggering depends on the angle of descent. 
At the low firing angle, the score on this test was 
about 60 per cent, while at high angle it was practi- 
cally zero. 


IONF1DENTIAL 


TEST OF FUZES MOUNTED ON BOMBS 87 





Table 4. Field tests 

on sunproofed units. 




Test No. 

No. of 
special 
fuzes 

No. of 
standard 
fuzes 

Firing 

elevations 

(degrees) 

Random 

Functions 

On sun On approach 

Dud 

1 

25 


20 

1 

1 

0 

23 



13 

20 

0 

12 

0 

0 



9* 

20 

0 

0 * 

1* 

8* 

2 

12 


61 

4 

1 

2 

5 



4 

61 


2 


2 



23 * 

61 

6* 

0* 

0* 

17* 

3 

13 


11 

0 

1 

7 

5 



2 

11 

0 

2 

0 

0 


•• 

21 * 

11 

0 * 

0 * 

13 * 

8* 


* Indicates control rounds fired at a time of day when, for the traj ectory chosen, the fuze could not see the sun. 


The development of sunproof fuzes required de- 
termination of the type of light signal seen by the 
fuze when it passes into the sun. The sun signal is a 
high-amplitude, low-frequency alternation, which is 
caused by rocket yaw. The following field-test infor- 
mation was obtained on the rate and amplitude of 
yaw of the M-8 rocket: 

1. Rockets equipped with smoke tracers were fired 
from an airplane and the trajectories were photo- 
graphed. 4 Measurements of the photographic rec- 
ords gave frequency of yaw, but not the amplitude. 
The average frequency of 11 rounds was 4.4 c. 

2. Yaw reporters (see Section 7.5) were built, in 
which the photocell current from a T-4 optical sys- 
tem determined an audio frequency, which modu- 
lated the reporter’s radio transmitter. The audio- 
frequency modulation was roughly proportional to 
the photocell current. The record from a single test 
showed an average yaw frequency of 3.5 c for the 
M-8 rocket. 20 The test was also expected to yield 
data on the amplitude of yaw, but the results were 
uncertain in this respect. 

3. An analysis of the sun angles at which T-4 
fuzes functioned when fired into the sun provided 
rough data on yaw amplitude. The results indicated 
an average yaw amplitude of about 9 degrees. 36 

During the development of sunproof modifications 
for the fuzes, a laboratory yaw test machine was 
built, which permitted roof tests to determine the 
behavior of fuzes while oscillating relative to the 
sun at any desired frequency and amplitude. The 
field data on yaw amplitude and frequency pro- 
vided a guide as to the minimum frequency and 
amplitude at which modified fuzes should be sun- 
proof on the yaw machine. 40 ' 42 


8,7,3 Results of Early Tests 

Reference is made to the bibliography for results 
of evaluation tests on earlier models of photoelectric 
rocket fuzes. 

Tests on low-sensitivity fuzes without amplifiers 
are covered in references 43, 44, and 48. Tests on a 
fuze with a three-stage amplifier (BR model, or 
M-l), intended for use on British 3.25-in. rocket, 
are covered in reference 46. The BR model became 
obsolete with the development of the one-stage 
model used in T-4 fuzes. 

Tests of fuze performance on rotating rockets are 
covered in references 24, 25, and 35. 

Reference 2 covers other miscellaneous tests. 

8 8 TEST OF FUZES MOUNTED ON BOMBS 
8,8,1 T— 4 on Bombs 

A special version of the T-4 was prepared for 
mounting on bombs. The nose of the fuze was 
mounted in a T-50 bomb fuze housing on the nose 
of the bomb. The battery and switch were mounted 
in a special bakelite housing in the tail of the bomb. 
A flexible cable, passing through a tube through the 
center of the bomb, connected the fuze nose to the 
battery and switch. The switch was modified to be 
actuated by withdrawal of an arming wire. 

This modification of the T-4 was intended for 
use in tests and training in the use of bomb-tossing 
equipment.® 

The modified fuzes operated satisfactorily on 
ground approach when dropped into wooded areas. 27 

When tested in toss bombing maneuvers against 

c See Division 4, Volume 2. 


CONFIDENTIAL 


5 


88 


EVALUATION OF PE FUZES 


a PQ-8 radio-controlled target plane the results in- 
dicated a lower than expected sensitivity. Otherwise 
performance was satisfactory. The low sensitivity 
(ROA of 15 ft) may have been due to a low ap- 
proach velocity. The amplifier of the T-4 fuze was 
designed to give optimum sensitivity at approach 
velocities somewhat over twice those encountered in 
this test. 30 

882 Generator-Powered Bomb Fuzes 

Only 15 generator-powered bombs were available 
for field testing before termination of the PE project. 
Two of these fuzes, designated T-52 or BPEG, were 
tested on M-57 and M-58 bombs by dropping into 
a wooded area. There were 8 proper functions and 2 
duds. 18 * 21 

Limited test of the self-destruction element in the 
BPEG fuzes show 100 per cent performance. 

883 Early Bomb Fuzes 

The initial period of photoelectric fuze develop- 
ment in this country was directed toward develop- 


ment of bomb fuzes intended for plane-to-plane 
bombing. The various models developed became 
obsolete after the development of the T-4 fuze and 
of generator power supplies. Results of proving 
ground tests on the early bomb fuzes are covered 
in detail in reference 1. 

A summary of the final evaluation tests on the 
first bomb fuze developed is of interest. These tests 
were made in September 1941. Twenty fuzes were 
dropped against a radio-controlled drone plane. The 
drone had a wing span of 25 ft and was painted 
bright yellow. The fuzes were dropped on Mark XII 
bombs with the bomber at 8,000 ft and the drone 
at 6,500 ft. Results were: 11 on target within pas- 
sage distance of 100 ft; 1 early; 5 self-destruction 
on rounds which passed too far from the target; 
and 3 duds. 

If self-destruction on passage at large radii, as 
well as target functions, are considered to be proper 
functions, the score on the 40 rounds of model C 
fuzes was 82 per cent proper. The radius of action 
against the small target was in the neighborhood 
of 100 ft. 


CONFIDENTIAL 


Chapter 9 

MISCELLANEOUS PROJECTS OF DIVISION 4 


91 ROCKET DEVELOPMENT b 

9,1,1 Test Rockets 

T o insure an adequate supply of rockets for its 
own use, Division 4, NDRC, then Section E, Divi- 
sion A, initiated the development of rockets in June 
1941. As a result, a satisfactory 3^i-in. rocket was 
developed and produced in experimental quantities. 
In addition, a target rocket (see Section 9.1.2), later 
used extensively in the training of antiaircraft crews, 
was developed. 

When Section E began the development of prox- 
imity fuzes for rockets, it was apparent that testing 
of the fuzes would require substantial numbers of 
rockets. Few British rockets were available, and only 
a few rockets per day were being made in this coun- 
try. All these were being used for experimental pur- 
poses by the rocket development groups. Thus, to 
insure an adequate supply of rockets for its own 
use, Section E began work on rockets. The initial 
plan was to design and to produce in small quanti- 
ties a satisfactory rocket to serve as a vehicle for 
the various rocket fuzes. No thought was given to 
the design of a rocket for use as a weapon. 

The early radio proximity fuze research program 
was based on the use of the British long-range 
rocket and the modified versions under development 
by Division 3, then Section H, Division A, NDRC. 
Certain physical sizes, such as the 3 %- in. diameter, 
were therefore fixed and carried through subsequent 
designs. 

A* number of designs of various lengths and nozzle 
diameters were made in the Bureau of Standards 
shops and tested statically and ballistically. The 
most satisfactory design was produced in sufficient 
quantity for preliminary rocket and fuze testing. 
As increased numbers were required, they were 
purchased from the Central Scientific Company of 
Chicago, Illinois. For purposes of coded reference, 
they were thereafter referred to as Cenco motors. 

a Most of the projects summarized in this chapter were 
either undertaken in cooperation with other divisions of 
NDRC or initiated by Division 4 and later transferred to 
other divisions. For these reasons, the projects in this chap- 
ter are described with more than usual historical detail. 

b This section was prepared by Clarence B. Crane of the 
Ordnance Development Division of the National Bureau of 
Standards. 


The motor was designed to be made from stand- 
ard stock material without special machinery. The 
body was made from 3%-in. OD by 0.120-in wall 
steel tubing closed at the forward end with a plug 
welded to the tube. At the nozzle end an annular 
internally threaded ring was welded. The nozzle 
was machined from solid bar stock threaded to fit 
into the ring welded to the tube. Four sheet steel 
drag fins % 6 x2 1 /2xl2-in. long were welded to the 
tube. The entire assembly was 24% in. in length. 6 

A wire cage, designed to hold the sticks of pro- 
pellant, was fastened to the inside of the closed end 
of the motor. This consisted of six %-in. diameter 
wires welded to a ring. Three sticks of propellant 
w r ere slipped onto each wire. A base plate was placed 
on the projecting ends of the wires, and two nuts 
were screwed onto each wire. The plate was then 
bolted to the inside of the rocket motor. This se- 
curely held eighteen sticks of %-in. OD by ^-in. ID 
by 5-in. long propellant, which was fired by an elec- 
tric detonator enclosed in a silk bag of black powder. 
A photograph of this rocket and its components is 
shown in Figure 1. 



Figure 1 . Test rocket (3.25 in.) showing motor body 
with fins attached and nozzle directly below. Loaded 
power cage, black powder igniter with enclosed electric 
detonator, bare wire cage, and representative samples 
of propellant are also shown. 


89 


L 


CONFIDENTIAL 


90 


MISCELLANEOUS PROJECTS OF DIVISION 4 


The shape of the nozzle is the most important 
part of the rocket design. 0 However, since the type 
of powder and the burning area exposed are the 
largest factors involved in the calculation of the 
nozzle diameter, the powder type and size available 
dictated this design. The nozzle therefore was made 
1% in. in diameter with an 18-degree included angle 
opening. 

Average values of the pertinent characteristics of 
this motor, when carrying a proximity fuze and 
fired at an angle of 45 degrees are as follows: 2 5 


Burning distance 40 ft 

Burning time 0.12 sec 

Max velocity (ft per sec) 675 

Acceleration (g) 175 

Range 10,000 ft 

Flight time 30 sec 


912 Target Rockets 

At the request of the Coast Artillery, a program 
to develop a rocket to be used as a training target 
for light antiaircraft weapons was initiated during 
August 1941. The development program was carried 
out jointly by Divisions 4 and 3 (then Sections E 
and H of Division A, NDRC) . All design and test- 
ing was conducted by the staff members of both 
organizations with all construction work centered 
in Division 4’s Central Laboratories at the National 
Bureau of Standards [NBS]. The requirements 
stated were that the rocket have a speed of 250 
to 300 mph, reach an elevation of 200 to 400 yd, and 
that visibility be increased to allow a firing range 
of 500 to 2,500 yd. 1 

Several of the rockets developed and made at the 
National Bureau of Standards for use as vehicles in 
the proximity fuze program were regarded as suit- 
able in so far as speed and range were concerned. 
Two methods to increase visibility were considered. 
The first idea was to increase the size of the fins to 
a point where they would be readily visible at the 
required range. The second idea was to attach a 
smoke trail which would burn during the greater 
part of the flight, giving off a dense, colored smoke. 
In some cases, both methods were used on a rocket. 
Noisemakers, such as bomb whistles, were also tried 
and discarded. 

After several trials, a semicircular fin with a 
radius of 10 in. was designed. Two sheets of light 
gauge tin plate, cut into semicircular form, were 

c For a full discussion of the problems involved, the reader 
should refer to the reports of Section H, Division A, NDRC. 


fastened together at the periphery to form an en- 
velope. This was slipped over a wood and metal 
frame which spread the open side of the envelope 
and resulted in a lightweight, streamlined rigid 
structure. Four fins were then fastened to each 
rocket by means of bolts welded to the rocket body. 
The fins were generally painted black, but trials 
were conducted with white, highway orange, and in 
some cases fins were left unpainted. 9 

Several sizes of Sy^-in. diameter motors were 
tried. The variation occurred in the nozzle diam- 
eter and length of motor. Amounts of powder used 
varied from 450 to 1,200 grams. To place the center 
of gravity at the forward end of the motor, various 
lengths of SV^-in. diameter steel tubing were added, 
terminating in a pointed steel ogive. This extension 
tube was later shortened, and the ogive was weighted 
with iron filings. 

At this point in the development, a test was con- 
ducted at Fort Monroe, Virginia, on October 11, 
1941. Eleven rockets with semicircular metal fins, 
and loaded with 1,140 grams of powder, were fired at 
an angle of 45 degrees. For the six good flights, the 
following data were averaged: 1 


Flight duration 
Range 

Initial velocity 
Velocity at top of trajectory 
Velocity at end of trajectory 
Angle of projection 
Angle at end of trajectory 


21 sec 
1,920 yd 
450 mph 
170 mph 
240 mph 
45 degrees 
63 degrees 


Four flights were satisfactory but shorter, having 
a flight of only 16.6 to 18.2 sec. One motor exploded 
after a flight of only 12.6 sec. 

The general opinion by observing Service per- 
sonnel was that the rockets as tested would be very 
useful for target practice. 

During this period some work had been done on 
a swaged nozzle. The Revere Copper and Brass 
Company had developed a method for mass produc- 
ing the motor by swaging a thin wall steel tube to 
form a nozzle. Section E ordered from this company 
a number of target rockets based on the design data 
previously discussed. The result is shown in Fig- 
ure 2. 

Because of the speed and range requirements, the 
motor was specified as a 14-degree lV 2 -in. diameter 
nozzle. The total length of the assembly was 66 in. 
The motor was 24y 2 in. long and 3*4 in. in diameter. 
A cast iron hemisphere, mounted in the end, placed 
the center of gravity 5 in. forward of the leading 


CONFIDENTS 


T-25 MORTAR SHELL 


91 


edge of the fin. The 4 half-circle fins were inter- 
changeable and readily mounted on the motor by 
clips and spring catches, making possible easy ship- 
ment and field assembly. Since the nozzle was 
formed directly in the tubing, the forward end was 
closed by an obturator cup, a steel plate, and a 
spring snap ring. The 7-wire powder cage was bolted 
to this closure plate. The forward end of the motor 
was threaded to connect directly to the body tube. 
Twenty-one sticks of propellant % in. OD by *4 in. 
ID by 5 in. long were fired by a squib or electric 
detonator enclosed in a silk bag with a small quan- 
tity of black powder. 

At this stage of the development, Section E with- 
drew from the problem, and further work was car- 
ried on by the Coast Artillery, the Ordnance De- 
partment, Section H, and the Revere Copper and 
Brass Company. Later developments resulted in a 
rectangular fin structure and a shorter assembly. 
Eventually only three fins were used. 


Figure 2. Target rocket assembled and ready for use. 

Use of these rockets in the training of antiaircraft 
crews had become standard procedure by the end of 
1942. All told, the Army procured and used several 
million such rockets. 

Launcher 

The Central Laboratories (NBS) then undertook 
the design of a launcher or projector from which to 
fire the target rocket. This involved a pair of guide 
rails mounted on an automotive trailer-type chassis, 
with provision for elevating the rails, electric con- 
nections, and good tracking characteristics for high- 
way towing. The guide rails were mounted on 
supports long enough to provide clearance for one 


fin to ride between the rails. The rail assembly was 
11 ft long, and a method was provided whereby it 
could be withdrawn and fastened to the tow bar, 
making a shorter trailer for towing. The projector 
set in firing position is shown in Figure 3. 7 > 8 



Figure 3. Target rocket projector in firing position. 


The L. and S. Welding Company of Baltimore, 
Maryland, received the first contract for the con- 
struction of a pilot lot. Engineers from the Bureau 
of Standards followed the initial production and, 
with the full cooperation of the contractor, success- 
fully completed the design. 

92 T-25 MORTAR SHELL d 

9,21 Introduction 

In connection with the development of radio prox- 
imity fuzes for trench mortar shells, 6 it was decided 
that the possible additional drag introduced by the 
special fuze might be appreciably reduced by re- 
designing the shell. It also appeared that redesign of 
the 81 -mm shell would greatly increase its stability 
in flight. Accordingly, a project was undertaken, in 
cooperation with the Engineering and Transitions 
Office of NDRC, to redesign the 81 -mm trench mor- 
tar shell. The redesigned shell was designated T-25. 

9 ' 2 ' 2 Difficulties with Standard Shells 

Requirements of the 81 -mm mortar VT fuze were 
(1) that the fuze be interchangeable with the me- 
chanical fuze without modification of the projectile, 

d This section was written by L. M. Andrews of the Ord- 
nance Development Division of the National Bureau of 
Standards. 

e See Division 4, Volume 1. 



confidential 



92 


MISCELLANEOUS PROJECTS OF DIVISION 4 


and (2) that the use of the VT fuze should have a 
negligible effect on the ballistics of the projectile. 
These requirements become major design factors 
for a mortar VT fuze. This was apparent from a 
comparison of the relative sizes of the smallest VT 
mortar fuze and the 81-mm shell, M43A1. The 
T-132 fuze was approximately 1 lb heavier than the 
point-detonating fuze, and this difference in weight 
amounted to more than 10 per cent of the total 
weight of the round. (See Figure 6, Chapter 1, for 
view of T-132 on mortar shell.) 

Since the minimum size and weight of the fuze 
were fixed by other factors, the ballistic problem 
resolved into a consideration of the aerodynamic 
drag and stability. It was probable that the VT fuze 
would change both these factors. A minimum drag 
is desirable in order to approach the corresponding 
range of the PD round. A high degree of flight sta- 
bility is a necessity; low stability would mean a 
large yaw in flight, or a tendency to tumble, with a 
resultant large dispersion, short range, and mal- 
function of the VT fuze. 

During the development of the mortar fuzes it 
became apparent that both of the above require- 
ments could not be met with the existing 81-mm 
Service shells. Both the M-43 and M-56 have only 
marginal stability with the bakelite or aluminum 
point-detonating fuzes. With all VT designs, the 
stability was unsatisfactory. Preliminary wind tun- 
nel measurements of drag and stability of mockup 
fuzes on the M-43 shell showed that the stability 
could be improved if the fuze had a large flat frontal 
area. 11 Later tests of various fuze models also indi- 
cated that perhaps satisfactory stability could be 
attained by use of a flat-nosed fuze. 12 

A flat front, however, has the disadvantage of 
increasing the drag by nearly 60 per cent, which in 
turn reduces the maximum range of the M-43 by 
30 per cent. From the viewpoint of good ballistics, 
it would have been desirable to streamline the fuze 
contour for minimum drag and to gain stability by 
some other means. One possibility was to increase 
the weight of the fuze. This has the effect of moving 
the center of gravity farther ahead of the center of 
pressure and thus increasing the restoring torque 
of the shell. The increase in stability is not as large 
as may be expected, since this also increases the 
transverse moment of inertia of the shell, and hence 
a larger restoring torque is required to control any 
initial yaw. Also, any appreciable increase in weight 


would reduce the maximum range as well as in- 
crease the size of the fuze. Another method of attain- 
ing stability would be modification of the shell by 
the substitution of a new fin system or extension of 
the present fin by means of an adapter; however, 
the requirement of no modification of the round 
ruled out the latter method at this time, and dic- 
tated the attempt of attaining stability by means of 
a flat-nosed fuze. 

Preliminary field tests of the M-43 with dummy 
fuzes indicated satisfactory stability; later tests of 
the T-132 fuze on the M-43 and M-56, however, 
showed an appreciable number of rounds with bad 
yaw and several instances of tumbling in flight. The 
range, of course, was comparatively short. Wind 
tunnel tests which were made on the T-172, another 
VT mortar shell fuze, indicated that it was still less 
stable than the T-132. 11 Modification of the fin sys- 
tem was a necessity with its use. Since it appeared 
very improbable that the ballistic properties of the 
standard PD fuze could be approached with any VT 
fuze design without modification of the shell, this 
last requirement was waived soon after experimental 
production was started on the T-132. 



Figure 4. Stability of M-43 shell with various fuzings 
and tail assemblies. 


With the M-43, two simple modifications were 
possible, either to extend the fin 2 in. by means of 
an adapter, or to replace the fin with that of the 
M-56. With the M-56 shell, it was also found that 


CONFIDENTIAL 


T-25 MORTAR SHELL 


93 


a 2-in. fin extension would result in satisfactory 
stability with either the T-132 or the T-172 fuze. 
Typical stability and drag characteristics of the two 
shells with various fuzes are shown in Figures 4, 5, 
and 6. In order to compare dissimilar shells, the 
stability has been expressed in terms of Kr/B, in 
which K is the restoring torque per degree of yaw, 
B is the transverse moment of inertia, and r is the 
distance from center of gravity to the end of the 



Figure 5. Drag of M-43 shell with various fuzings 
and tail assemblies. 


stabilized fin. 15 Figure 4 shows the effect of the 
T-132 fuze on the stability of the M-43 with and 
without fin extensions, as well as the effect of par- 
tially streamlining the fuze. The T-132B fuze is 
identical with the T-132 except for a slightly smaller 
diameter turbine and a partially streamlined tur- 
bine cover. Corresponding drag curves are shown in 
Figure 5. The M-56 characteristics are shown in 
Figure 6. The 2-in. fin extension of magnesium alloy 
weighs approximately 0.1 lb, and hence has little 
effect on the weight of the shell. It is apparent that 
stability can be increased by this means with very 
little increase in drag and/or in weight; in fact, it 
allows the fuze to be further streamlined for mini- 
mum drag. Range tests indicate that, if the drag of 
the YT fuze could be reduced to the same value as 
that of the PD fuze, the maximum range of the 
M-43 would be only 5 per cent less due to the dif- 
ference in weight. 13 



Figure 6. Stability and drag of M-56 shell with 
various fuzings. 


9 - 2 - 3 T -25 

Another solution to the ballistic problem was the 
use of a new shell so designed that it would be stable 
with either the PD or VT fuzes, without modifica- 
tion. We have seen that the desired interchange- 
ability could not be attained with either of the 
existing 81 -mm shells. Although the M-43 and M-56 
could be made stable by changes in the fin system, 
there are other objections to the use of the modified 
shells. The M-43 has a relatively small HE capacity, 
and hence there is a question of the economics of its 
use with the VT fuze. M-56, on the other hand, has 
a relatively short range. The opportunity of improv- 
ing the ballistics of the shell presented itself when 
members of the Engineering and Transitions Office 
suggested that, in connection with its program of 
setting up new facilities for mortar shell production, 
it would be possible to experiment with a new shell. 
Accordingly, the Bureau of Standards was asked to 
submit a design for an 81 -mm mortar shell with im- 
proved ballistic properties, without too much sac- 
rifice in HE capacity or range. 

The time factor was the main element of control. 
Other design factors were the availability of the 
M-56 aluminum fin assembly with good ballistic 


CONFIDENTIAL 



94 


MISCELLANEOUS PROJECTS OF DIVISION 4 


characteristics, and the desirability of using a rela- 
tively thin wall. Panel tests had indicated that for 
fragmentation purposes the thin wall of the M-56 
was more efficient per pound of weight than the 
heavier wall of the M-43. 

For long range, the shell must be well streamlined. 
Since it was desirable to use the M-56 fin system 
and a thin-walled shell, the length of the body be- 
came the controlling factor of both weight and sta- 
bility. Maximum range, in turn, depended primarily 
on the weight. As neither the desired range nor 
weight were specified, an arbitrary compromise was 


made by tentatively fixing the length of the body 
at 12 in. This resulted in a shell approximately 3 in. 
shorter than the M-56, with 75 per cent of its HE 
capacity, and weight midway between that of the 
M-43 and the M-56. 

Preliminary models were made of 2 types, differ- 
ing only in the nose contour, as shown in Figure 7. 
Type X has a nose contour identical with that of 
the M-56, whereas Type Y is more like the M-43. 
Wind tunnel tests were carried out to determine 
drag and stability of these models with the PD and 
VT fuzes. The results were very encouraging. The 



Figure 7. Proposed contours for T-25 mortar shell. 

CONFIDENTIAL 


T-25 MORTAR SHELL 


95 


new shell showed better stability than either the 
M-43 or the M-56 even when these shells were 
modified by means of a 2-in. fin extension. Aero- 
dynamic drag promised not to be nearly as low as 
that of the M-43. It would have been advantageous 
to carry out further wind tunnel tests to study the 
effect of other body contours and lengths upon bal- 
listics. However, time did not permit this. The con- 
tour designs, as shown in Figure 7, were submitted 
to OSRD 3 days after the assignment. The shells 
were shown without the bourrelet, as it was antici- 
pated that this feature might be eliminated by means 
of the proper shell diameter. (This was later verified 
by range tests at the Clinton Proving Ground at the 
University of Iowa, on modified M-56 shells.) Other 
factors, such as exact wall thickness and inside con- 
tour, must of necessity be determined by field test 
and, to some extent, by manufacturing expedients. 
Since there was very little difference between the 
Type X and Y shells aerodynamically, the choice of 
contour would depend on the desired fragmentation 
or penetration properties. 14 

Under the direction of the Engineering and Tran- 
sitions Office, 20 experimental lots of the T-25 shells 
were made at the Kewaskum Aluminum Company, 
each lot differing in either nose contour, wall thick- 
ness, inside contour, or length. For the purpose of 
fragmentation tests, wall thicknesses were varied 
from approximately 0.075 to 0.130 in. Except for 
lots 18 and 12, all shells were either of the X or Y 
type. Lot 18 was made with the body length of 11 in. 
instead of 12 in. Lot 2 was made with a very blunt 
nose contour with an outside radius of approximately 
1 in. 

Samples of each of the lots were analyzed at the 
National Bureau of Standards for ballistic proper- 
ties with the PD and VT T-132 fuzes. 15 ' 18 Metal- 
lurgical tests were also performed on the steel. 19 As 
the shells were made with temporary tools and did 
not represent the desired product in several minor 
respects, only a preliminary comparison could be 
made of the various types. Slight irregularities of 
contour may have an appreciable effect on drag and 
on the location of center of pressure. In general, the 
wind tunnel tests substantiated the measurements 
on the preliminary models. Due to conservative es- 
timates of the center of gravity of the models, sta- 
bilities proved to be even higher. If stability is 
expressed in terms of the ratio of the distance be- 
tween the center of pressure and the center of gravity 


to the overall length, the T-25 shells have a factor 
of 12 to 13 per cent with either PD or VT fuzes. This 
is to be compared with 7 per cent for the M-43 with 
a PD fuze, and 11 per cent with the T-132 fuze and 
a 2-in. fin extension. Stability of the M-56 is even 
lower than that of the M-43. Variations in wall 
thickness and nose contour, as represented by the 
various lots tested, had but slight effect on sta- 
bility. 16 - 17 

Figure 8 shows graphically the stability of the 
T-25 shells compared with the M-43 and the M-56. 
The effect of a further compromise in weight of the 
round in order to gain range was shown by lot 18. 
With a body length of 11 in., the drag is reduced to 



O 4 8 12 16 20 

ANGLE OF YAW (DEGREES) 

Figure 8. Stability of models of T-25 mortar shell, 

shown in comparison with M-43 and M-56 shells. 

that of the M-43. A shell of this length, with a wall 
thickness of 0.080 in., would have approximately the 
same weight and range as the M-43, but with more 
than double its HE capacity (capacity is 68 per 
cent of that of the M-56). Stability is, of course, 
further increased by the reduced body length. 

Shells of the lot 2 type proved of interest also. 
This shell, with a relatively blunt nose, should have 
a better fragmentation pattern. The drag as meas- 
ured at 100 ft per sec showed no increase over that 
of the other shells. 

All the wind tunnel tests indicated that a shell of 
the T-25 type, regardless of the exact wall thickness 
or nose contour, should have a very stable flight 
with any of the present PD or VT fuzes. The tests 
also showed that a T-25 shell would allow for com- 


GONFIDENTIAL 


96 


MISCELLANEOUS PROJECTS OF DIVISION 4 


plete streamlining of the VT fuze; hence the differ- 
ence in range of the PD and VT rounds could be 
reduced to a minimum. 

Range tests of a small number of lots 3, 12, and 17 
shells were attempted; however, the data were in- 
sufficient for reliable comparisons. 10 A maximum 
range of approximately 3,300 yd at 5 increments of 
charge was indicated. Due to the limited data, no 
estimate of dispersion could be made. A complete 
evaluation of the T-25, including fragmentation, 
range, and dispersion data, had not been completed 
at the end of World War II. f 

9.3 THE magnetic field machine b 

9-3-1 General 

The magnetic field machine is an apparatus that 
was developed for the use of the Naval Ordnance 
Laboratory in connection with the protection of 
ships against magnetic mines. The design, construc- 
tion, testing, and operation of the machine is fully 
covered in reference 20, and only a brief description 
of the main features is given here. The first machine 
was installed in the Naval Ordnance Laboratory in 
April 1941. Subsequently, the Navy ordered addi- 
tional machines for other locations. 

9 - 3 - 2 The Problem and General 

Character of Its Solution 

The machine was developed to provide a physical 
solution to a type of problem that had, for want of 
an easier method, been solved previously by tedious 
mathematical calculations. The problem is to deter- 
mine the magnetic field intensity of a ship through- 
out a large volume of water underneath the ship, in 
order to determine whether the ship can pass safely 
over a magnetic mine. Magnetic mines of current 
design are lodged on the ocean bed and operate when 
influenced by any change in excess of a certain 
minimum change in the vertical component of mag- 
netic intensity. The basic magnetic measurements 
that are made on a ship provide a map of the vertical 
component of magnetic intensity in a single horizon- 
tal plane slightly below the keel of the ship. If this 
plane is mapped over an area large enough so that 
there is a negligible total flux outside the mapped 

f For further information on the T-25 shell, reference is 
made to reports of the Engineering and Transitions Office. 

g This section was written by T. N. White of the Ordnance 
Development Division of the National Bureau of Standards. 


region, the field strength at all lower levels can be 
calculated from well-established laws of mathemati- 
cal physics. The magnetic field machine was de- 
signed to reproduce, on a small scale, the field in the 
mapped plane, and hence (on the same small scale) 
the field at all lower levels. The machine incorpo- 
rates search coils on an automatically driven car- 
riage, and an automatic recorder for mapping the 
field throughout the useful range of lower levels. 

9-3-3 Arrangements for Construction 
and the Overall Result 

The construction of a magnetic field machine was 
first proposed by the Naval Ordnance Laboratory 
to Division A of the National Defense Research 
Committee in November 1940. A general considera- 
tion of design problems by the physicists of this 
division led to a plan of construction that involved 
many problems which arise in telephonic engineer- 
ing. The basic design problems were presented to 
engineers of the Bell Telephone Laboratories in 
December 1940, and the detailed design and con- 
struction were worked out in collaboration with this 
company and the Western Electric Company. Test- 
ing was conducted at the National Bureau of Stand- 
ards. The complete equipment and typical results 
were formally exhibited in April 1941. The results 
of tests of the machine indicated that the ratio of 
overall time required for the solution of ships’ fields 
by the two methods — mathematical and physical — 
is between 10/1 and 20/1 in favor of the physical 
method. 

9-3,4 Basic Design Considerations 

An alternating magnetic field method was chosen 
on account of the ease of exploring the field with a 
small search coil, and its freedom from the effects 
of stray steady magnetic fields. A frequency of 270 c 
(180-pole alternator directly coupled to a standard 
4-pole synchronous motor on 60-c power) was se- 
lected to avoid harmonics present in 60-c power 
supply. The field intensity in the ship’s plane of 
measurement was reproduced by a stack of 4-ft 
single-layer coil solenoids 40 coils long by 20 coils 
wide (800 solenoids total). Hard rubber cores of 
rectangular section (1^4x% 6 in*) with longitudinal 
ventilating slots were used. In order to avoid phase 
shifts due to coupling between coils, a high ratio of 
resistance to reactance was obtained by using fine 
alloy wire No. 37, tinsel-bronze, 168 turns per inch. 


I 


CONFIDENTIAL 




RADAR RANGING ON SHELL BURSTS 


97 


The resulting rather low current avoided contact 
difficulties in the associated switching mechanism. 
Power was supplied to the coils through a “panel 
bank” (modified from standard automatic telephone 
exchange equipment) from a special tapped trans- 
former (center-tapped 60-volt secondary with taps 
every 0.3 volts each side of center) . Three search coils 
(to allow mapping of all 3 magnetic field compo- 
nents if desired) were mounted on a belt-driven car- 
riage. The output of any one search coil could be 
automatically recorded on a run through the mag- 
netic field. The recorder was of the self-balancing 
potentiometer type, especially designed by the Bell 
Telephone Laboratories for an accuracy of 0.01 mil- 
livolt. The output of the search coil was balanced 
against a reference voltage obtained from the tapped 
transformer to minimize the effect of power supply 
variations. 

9 ’ 3 ' 5 Sample Results 

Results obtainable with the machine are illus- 
trated in Figure 9. The field of the ship from which 
the basic data were obtained was also computed by 




Figure 9. Sample signatures taken from field of ship 
(TU-12) which had already been solved by computa- 
tion. (A) shows magnetic field as function of distance 
along ship at depth of 70 ft and 10 ft to starboard. 

(B) shows field of same ship at same depth but 130 ft 
to port. 

the mathematical method, and these results are 
represented by dots on the diagram. It will be noted 
that the pattern of the computed intensities is some- 
what more irregular, but the general agreement is 
very good. It is not known whether the differences 
arise from a slight “smoothing out” process inherent 


in the machine, or from irregularities arising from 
the assumption of discrete magnetic poles for the 
purpose of mathematical computation. There is 
fairly good reason to believe that the true field may 
be slightly less irregular than that given by the 
machine. 

9 4 RADAR RANGING ON SHELL BURSTS h 

Early in World War II, the British were report- 
ing observations of radar echoes from shell bursts. 
Later our own radar operators reported the same 
phenomena. This led to an interest in the possibili- 
ties of ranging on shell bursts by radar means as an 
effective method of fire correction. Division 4 was 
requested by the Navy 21 to consider this application 
of radar to fire control and to make the necessary 
experimental investigations to evaluate its effective- 
ness. Work started in February 1942 and was 
stopped in October 1942, before completion, because 
of conflict with the effective prosecution of the prox- 
imity fuze development. 

During this period, the available literature on the 
subject was abstracted, a program of investigation 
established, and several interesting experiments com- 
pleted. 22 ’ 23 The objectives were twofold: (1) to 
determine the mechanism of echo production; (2) 
to specify proper shell fillers and radar equipment 
for most effective burst ranging. Objective (1) had 
not yet been reached when Division 4 found it nec- 
essary to stop the work. 

The experimental program was run in close co- 
operation with Re4a of the Navy Department. The 
Navy provided facilities at Dahlgren, Virginia, and 
arranged for tests at Marine Barracks, New River, 
North Carolina, and at Camp Davis, North Caro- 
lina. 

First preliminary experiments were made at Dahl- 
gren, Virginia, to observe the echo from a static 
burst by means of continuous wave reflection. The 
echo was observed 22 and found to be of sufficient 
duration so that it could not be lost between radar 
pulses. This demonstrated that the echo observation 
did not appear to be a chance phenomenon. 

In parallel with the c-w experiments, some theo- 
retical work was done to see if ionization or frag- 
ments were the most probable source of the echo. 
It was decided that ionization probably accounted 
for most of the observed effect at low frequencies 

h This section was written by Robert D. Huntoon of the 
Ordnance Development Division of the National Bureau of 
Standards. 






98 


MISCELLANEOUS PROJECTS OF DIVISION 4 


(100 to 200 me) and that fragments might be more 
important at microwave frequencies (3,000 me). In 
the intermediate region, both might play a part. 

In addition to providing the facilities at Dahlgren, 
Virginia, for the c-w tests, the Navy arranged for an 
SCR268 (200-mc) fire control radar with a 3-in. 
AA gun and 25 special rounds filled with magnesium 
powder. 22 The tests were made at Marine Barracks, 
New River, North Carolina. Arrangements were 
made to photograph the echo pulses on the range 
oscilloscope. Of 18 rounds fired for the record, with 
slant ranges varying from 7,000 to 12,000 yd, 1 failed 
to burst and 17 gave good echoes. The echo per- 
sistence was from 0.08 to 0.22 sec, indicating that the 
ionized flash was probably responsible for the echo. 
The radar did not respond to the shell in flight. 
Fluctuations of echo intensity during the echo inter- 
val were observed. 

At the conclusion of the New River tests, a pro- 
gram for further investigation was suggested. 22 It 
involved three radar installations in the 200-, 700-, 
and 3,000-mc bands. Simultaneous observations on 
shell bursts were to be made with all three equip- 
ments. 

The Navy arranged with the Field Artillery 
Board to make these tests at Camp Davis, North 
Carolina. About 120 rounds of ammunition were 
available with 21 different fillers in the high explo- 
sive. The results were contrary to experience re- 
ported by British observers. 

The SCR268 (200-mc) received echoes from all 
fillers at all ranges and worked about as well on 
pure TNT as on complicated fillers. The echo was 
similar to that previously observed. 

The Navy FD (700-mc) followed the shell from 
the firing point, and observed a strong flash echo at 
the instant of burst, followed by a weaker persistent 
echo lasting from 15 to 30 sec. There were periodic 
variations of amplitude during the persistent echo. 
There was no observed agreement between filler and 
echo persistence. The flash echoes were better with 
some fillers than others. The exact details will be 
found in reference 24. 

The MIT radar XT-1 (the 3,000-mc prototype of 
the SCR584) did not give useful echoes on any of 
the bursts at any range. There was considerable 
difficulty with this prototype equipment and there 
was no guarantee that the lack of echo from the 
bursts was a true phenomenon. The results with the 
XT-1 equipment were therefore inconclusive. 


At this interesting stage of the experiments, Divi- 
sion 4 discontinued participation in the project. 1 
Work was continued by the General Electric Com- 
pany under contract to the Navy Department. 

95 CONTROLLED-TRAJECTORY BOMBS 
9,51 The Basic Problem 

The development of a controlled-trajectory bomb 
having a glider-type attachment with adjustable 
control surfaces was initiated in Section E in Janu- 
ary 1941. In December 1942, when Section E became 
Division 4, the project was transferred to Division 5. 
By the time of the transfer several models had been 
built and tested successfully in the field. 

It appeared that improved accuracy of bombing, 
especially from high altitudes, could be obtained by 
using technical advances in radio, television, and 
aerodynamics to control the trajectories of bombs 
in flight. 

The technical problems involved in controlling 
trajectories fell into three general categories as fol- 
lows: 

1. Means for indicating to the bombardier the 
need of control. Although there were many possible 
means for doing this, the most attractive solution 
appeared to be the use of television equipment in 
the bomb. The television picture would be trans- 
mitted by radio from the bomb to the bombardier, 
giving him the view ahead which he would have if 
he were actually riding on the bomb. 

2. Means of communication between the bombar- 
dier and the control mechanism. The most practical 
solution to this problem appeared to be the use of a 
radio link. 

3. Method of applying forces to the bomb to mod- 
ify its trajectory. Although rocket control was sug- 
gested early and would have been possible, it was 
thought to involve additional and unnecessary com- 
plications. By far the most common and practical 
suggestion and the one that was adopted was to 
modify the aerodynamic forces on the bomb by 
changing the bomb’s shape, that is, by turning a 
rudder which caused the bomb to assume a new 
orientation. 

In addition the glider bomb itself would have to 
be developed. It would have to have the following 
characteristics: 

1. Good flight characteristics. The problem of 

‘For additional information concerning this project, see 
references 25 through 35. 


CONFIDENTIAL 


SUBSTITUTES FOR SILK IN POWDER BAGS 


99 


dynamic stability later proved to be the most serious 
aerodynamic problem and received foremost atten- 
tion for nearly two years. 

2. Capacity for large explosive charge. It was 
generally agreed that the cost of the control equip- 
ment would be such that nothing less than the equiv- 
alent of a standard general purpose 2,000-lb bomb 
should be considered and that, for many purposes, 
a larger weight would be desirable. It was decided 
early to take advantage of the large amount of work 
that had gone into the design of high-explosive 
bombs of the ordinary type by using a standard 
bomb as the component explosive part of the 
weapon. 

3. Ease of storage and handling properties. The 
dimensions should be such that it could be carried 
on airplanes both while they were in flight and dur- 
ing take-off and landing operations. Although the 
use of towed glider bombs would have removed most 
size restrictions, it was felt that towed gliders would 
introduce many new and difficult aerodynamic prob- 
lems relating to their stability and control. 

Progress of Development 

The development of a suitable aerodynamic struc- 
ture for the glider bomb was the first problem to be 
undertaken. Scale models of a proposed structure 
were built and equipped with controls operated by 
a radio link. The first models were completely un- 
stable, but, after extensive wind tunnel tests, a 
satisfactory aerodynamic design was achieved. 

In parallel with the structural design, a television 
viewing set was developed. This weighed less than 
100 lb and occupied about 2 cu ft. By June 1942, 
satisfactory field tests of glider bombs equipped 
with television sets were obtained. 

Limitations of the television equipment to day- 
light operation were appreciated, and projects were 
initiated to remove this deficiency. One method was 
to provide suitable flares for illumination of the 
target at night, another was the development of 
radar bombing equipment. These projects were just 
getting well underway when, with the reorganization 
of NDRC in December 1942, further work was as- 
signed to Division 5. Work completed under Divi- 
sion 4 (then Section E) direction is covered in detail 
in references 36, 37, and 38. J 

j For information concerning the successful consummation 
of the project, leference is made to the reports of Division 5. 


9 6 SUBSTITUTES FOR SILK IN 

POWDER BAGS 39 > 40 < 41 

The Armed Forces of the United States have used 
silk for making cartridge bags for large-caliber guns, 
largely because this fabric has greater resistance to 
progressive combustion and afterglow than do other 
common fabrics. The supply of silk was depleted 
with the beginning of the war with Japan, and a 
satisfactory silk substitute was sought, cotton re- 
ceiving greatest attention because of its comparative 
abundance. Division 4 undertook work on the prob- 
lem, utilizing textile experts at its central labora- 
tories, the National Bureau of Standards. 

Desired characteristics included flame resistance, 
adequate strength and resistance to deterioration, 
lack of smoldering and afterglow, as complete com- 
bustibility as practicable, and only moderate hygro- 
scopicity. 

Many materials with which cotton might be 
treated were known to have some of these charac- 
teristics, but were rejected because they were also 
known to lack others or because they were in critical 
supply. 

Treated cotton fabrics were subjected to a num- 
ber of tests to determine their flame and smolder 
resistance, hygroscopicity, resistance to aging and 
to deterioration by oxides of nitrogen. Weighted 
scores were compiled from these tests, greatest value 
being given to the characteristics considered most 
important. 

One fabric was rated superior to silk, and two 
others were found nearly equal to silk. Of the 6 
types tested, the material receiving the highest score 
was cotton treated with urea, hexamethylene tetra- 
mine, and ammonium dihydrogen phosphate. With 
a theoretically perfect material scored at 100, this 
treated cotton scored 73 as against a score of 71 
for silk. 

The material with the next highest score (69) was 
cotton treated with ammonium sulphate, urea, hexa- 
methylene tetramine, and dibasic ammonium phos- 
phate. A score of 68 was obtained when the cotton 
was treated with urea, hexamethylene tetramine, 
and ammonium ethyl-orthophosphate, the last a 
commercial product. 

However, if the method of weighting is changed, 
one of the other treatments may be found preferable 
to that which received the highest rating with the 
weights given. 39 


CONFIDENTIAL 













































































































































































































. 



















































BIBLIOGRAPHY 


Numbers such as Div. 4-212-MI indicate that the document listed has been microfilmed and that its title 
appears in the microfilm index printed in a separate volume. For access to the index volume and to the microfilm, 
consult the Army or Navy agency listed on the reverse of the half-title page. 


Chapter 2 

NDRC ARMOR AND ORDNANCE REPORTS 

1. The Photoelectric Fuze as of November 4, 1940, 
L. R. Hafstad, NDRC Report A-l, November 1940. 

Div. 4-212-MI 

2. Measurements of Electric Fields near Airplanes in 
Flight, E. J. Workman, NDRC Report A-7, June 1941. 

Div. 4-750-MI 

3. Studies of Acoustic Proximity Fuzes, J. A. Reardon, 
NDRC Report A-12, July 1941. Div. 4-213-MI 

4. Acoustic Proximity Fuzes, Richard K. Cook and W. C. 
Mock, Jr., NDRC Report A-23, Dec. 4, 1941. 

Div. 4-213-M2 

5. The Barotimer — A Barometrically Set Time Fuze, 

S. K. Allison, W. P. Jesse, and T. J. O’Donnell, NDRC 
Report A-26, Jan. 1942. Div. 4-214-MI 

6. Radio Reporters for Proximity Fuze Testing, A. V. 
Astin, NDRC Report A-53, May 1942. Div. 4-611-MI 

7. Continuously Adjustable Electric Time Fuze, W. F. 
Westendorp, NDRC Report A-l 14, Nov. 11, 1942. 

Div. 4-215-MI 

8. Airbursts for Blast Bombs, E. B. Wilson, Jr., NDRC 

Report A-322, April 1945. Div. 4-242. 12-M4 

MISCELLANEOUS REPORTS, DIVISION 4, NDRC 

9. An Adjustable Time Fuze Using Resistance-Capaci- 
tance Discharge Circuit, C. A. Moreno, War Research 
Laboratory, University of Florida, Jan. 6, 1945. 

Div. 4-215-M2 

10. A Study of the Dielectric Properties of Dielectric 
Materials Made from Mixtures of Titanium Alloys, 
D. C. Swanson, W. H. Beisler, and R. D. Walker, 
University of Florida, Sept. 2, 1945. Div. 4-239.3-MI 

11. Study of Condensers with Solid and Liquid Dielectrics, 

H. L. Knowles and D. C. Swanson, University of 
Florida, Jan. 19, 1944. Div. 4-237-M2 

12. Interim Report, February 15 to March 7, 1945, A. V. 
Astin to Dr. Alexander Ellett. 

ARMY REPORTS 

13. The Optimum Point of Burst for a 500-lb GP Bomb 
Equipped with a Proximity Fuze, Marston Morse, 
Wm. R. Transue, and Roy Kuebler, TDBS 7, Office 
of the Chief of Ordnance, Apr. 22, 1943. 

14. The Dependence of Optimum Height of Burst of Shells 
and Bombs upon Angle of Fall, Safety Angle, etc., 
Marston Morse, Wm. R. Transue, TDBS Report 41, 
Office of the Chief of Ordnance, Sept. 2, 1944. 

15. Optimum Height of Burst of Fragmentation Bombs 
and Effect with VT Fuzes, Marston Morse, Wm. 
Transue, and M. H. Heins, TDBS Report 58, Office of 
the Chief of Ordnance, Apr. 3, 1945. 


16. Probable Advantages of VT Fuzes on 81 -mm HE 
Mortar Shell M-56 and M-43A1, Marston Morse, 
Wm. R. Transue, M. H. Heins, TDBS Report 60, 
Office of the Chief of Ordnance, Mar. 30, 1945. 

17. A Comparison of Damage Effect of Ground Bursts of 
20-lb Bomb with an Air Burst of the 260-lb Bomb and 
of the 500-lb Bomb against Planes and Revetments, 
TDBS Report 61, Office of the Chief of Ordnance, 
Apr. 24, 1945. 

18. Second Interim Report on Fuze, Bomb, T-50, Report 
of the Army Air Forces Proving Ground Command on 
Project 4012C4712.82, Apr. 12, 1945. 

19. Supplemental Tests on Aircraft Rockets for Anti- 
Personnel Effects, Report of the Army Air Forces 
Proving Ground Command on Project 4514C471.94, 
Sept. 4, 1945. 

BRITISH REPORTS 

20. Trials with an M64 500-lb Bomb, Nose Initiated, Fuze 
No. T50 against Close Support Targets, B. L. Welch, 
Appendix to Proceedings No. Q-2881, Ordnance Board, 
Dec. 13, 1944. 

/ 

Chapter 3 

1. Notes on Conference of 12 August 1940 between 

Representatives of NDRC and BuOrd, C. Hoover, 
Aug. 17, 1940. Div. 4-100-MI 

2. Initiation of Procurement of PE Fuzes for British 
3-Inch UP Rocket, Ordnance Committee Minutes 
17426, Nov. 4, 1941. 

3. Development of Anti-Aircraft Fuzes for Rockets, 
Initiation of Project, Ordnance Committee Minutes 
18178, Apr. 24, 1942. 

4. Initiation of Development Project for T-50, T-51 and 
T-52 Fuzes, Ordnance Committee Minutes 21117, 
July 17, 1943. 

5. The Photoelectric Proximity Fuze as of November 4, 

1940, L. R. Hafstad, NDRC, Armor and Ordnance 

Report 1. Div. 4-212-MI 

6. The Photoelectric Proximity Fuze, L. R. Hafstad et al., 
NDRC Armor and Ordnance Report A-20, Oct. 20, 

1941. Div. 4-212. 1-MI 

Chapter 4 

ARMOR AND ORDNANCE REPORTS 
DIVISION 4 , NDRC 

1. The Photoelectric Proximity Fuze, L. R. Hafstad et al., 
NDRC Report A-20, Oct. 20, 1941. Div. 4-212.1-MI 

la. Ibid., General Considerations and Part /^Section 
5, pp. 30-39. 

lb. Ibid., General Considerations and Part I, Section 
7, pp. 63-71. 


CONFIDENTS 


101 


102 


BIBLIOGRAPHY 


lc. Ibid., General Considerations and Part I, Section 
7, p. 65. 

l d. Ibid., Part I (Continued), Section 30, p. 356. 

REPORTS OF THE ORDNANCE DEVELOP- 
MENT DIVISION OF THE NATIONAL 
BUREAU OF STANDARDS 

2. The Photoelectric Proximity Fuze for Rocket Projec- 

tiles, S. H. Neddermeyer, unpublished report, Vol. 2, 
Sec. 1, pp. 14-17. Div. 4-212.2-M6 

3. Light Level Values for the North Sky, R. Stair and 
W. E. Williams, Report OD-2-12, July 3, 1943. 

Div. 4-248-M4 

4. Estimates of Damage to Military Aircraft from a 
Head-on Burst of HVAR 5" Rocket Shell as a Func- 
tion of the Radius of Action of the Fuze, B. M. 
Bennett, Report OD-OAG-54, Jan. 8, 1945. 

Div. 4-412. 3-M4 

MEMORANDA OF THE ORDNANCE DEVEL- 
OPMENT DIVISION OF THE NATIONAL 
BUREAU OF STANDARDS 

5. Measurement of Light Intensities at Altitudes up to 

25,000 Feet, Sept. 14, 1942. Div. 4-248-M3 

6. Pulse and Frequency Characteristics of MC-380 

Amplifiers, Memorandum to A. V. Astin from S. H. 
Neddermeyer, Mar. 31, 1943. Div. 4-238.221-M2 

CONTRACTORS OF DIVISION 4, NDRC 

7. View Angle and Look-Forward Angle of MC-380 A, 

K. D. Smith, Bell Telephone Laboratories, Nov. 7, 
1942. Div. 4-222 .224-M2 

8. Probability that a 4 %" Rocket Fired from Astern 
Will Destroy a Twin Engine Bomber ( Ju-88 ) as a 
Function of the Point of Burst, OEMsr-618, Statistical 
Research Group to the Applied Mathematics Panel, 
Columbia University, AMP Report 21. 1R, July 1944. 

Div. 4-412.3-MI 

U. S. MILITARY PUBLICATIONS— ARMY 
ORDNANCE 

9. Fragment Distribution and Fragment Velocity of 4%" 
HE Shell, M8, N. A. Tolch, Report 344, Aberdeen 
Ballistics Laboratory. 

Chapter 5 

ARMOR AND ORDNANCE REPORTS, NDRC 

1. The Photoelectric Proximity Fuze, General Considera- 
tions and Part I, Volumes I and II, L. R. Hafstad 
et al., NDRC Report A-20, Dec. 20, 1941. 

Div. 4-212.1-MI 

2. The Status of the Photoelectric Proximity Fuze for 
Rockets on March 13, 1942, NDRC Report A-44, 
Pilot Photoelectric Fuze Development Group at the 
National Bureau of Standards, Mar. 16, 1942. 

Div. 4-212.2-M2 


REPORTS OF THE ORDNANCE DEVEL- 
OPMENT DIVISION OF THE NATIONAL 
BUREAU OF STANDARDS 

3. The Photoelectric Proximity Fuze for Rocket Projec- 
tiles, J. E. Henderson, S. H. Neddermeyer, et al., 
unpublished report, Vols. I and II, 1942. 

Div. 4-212.2-M6 

4. Testing of Pentodes, R. A. Becker, Apr. 28, 1942. 

Div. 4-231. 4-MI 

5. Gas Currents and Input Impedance of HY145YT, 

R. A. Becker, Aug. 1, 1942. Div. 4-231.4-M2 

6. Report of Centrifuging of 24 HY-145-YT Pentodes to 
2000 g, R. A. Becker and C. Ravitsky, Sept. 19, 1942. 

Div. 4-231. 4-M3 

7. Progress Report on a Double Photocell Photoelectric 
Unit, R. Hofstadter, Nov. 11, 1942. Div. 4-231.51-MI 

8. Progress Report on Operation of a Single-Stage Unit 

without a B Battery, R. A. Becker and C. Ravitsky, 
Nov. 11, 1942. Div. 4-232.1-M4 

9. Progress Report #2 on Condenser-Driven Single-Stage 

Photoelectric Unit, R. A. Becker, C. Ravitsky, and 
D. Feldman, Dec. 14, 1942. Div. 4-212.3-M2 

10. Report of Test of 100 Assembled MC-380B Fuzes for 

Conformity to the September 30, 1942 Issue of MC-380 
Fuze Specifications (NDRC), Joseph E. Henderson, 
Dec. 21, 1942. Div. 4-222 .224-M3 

11. Effect of Light and Heat on Photocell Sensitivity, 

W. E. Williams, Jr., Memorandum Report 3-P, Jan. 
15, 1943. Div. 4-231. 5-M4 

12. Fuze, Rocket, PEP Condenser-Powered, Westinghouse, 
N Range, Corncake, March 4 and 5, 1943, R. Vorkink. 
Memorandum Report 108-T, Mar. 23, 1943. 

Div. 4-222 .222-M4 

13. Test of Reserve Batteries at Comcake, March 10, 1943, 

A. V. Astin and A. W. Spinks, Memorandum Report 
117-T, March 24, 1943. Div. 4-232.1-M5 

14. Pulse and Frequency Characteristics of MC-380 
Amplifiers, Seth H. Neddermeyer, Mar. 31, 1943. 

Div. 4-238 .221-M2 

15. Heater Cathode Pentodes, preliminary report, D. 

Feldman, Apr. 5, 1943. Div. 4-231. 4-M9 

16. Use of Polymerized Tung Oil for Potting MC-380 and 

MC-382 Fuzes, C. Brunetti and P. J. Franklin, Apr. 
29, 1943. Div. 4-239.1-MI 

17. Preliminary Report on Adaptation of the Photoelectric 

Fuze to a Generator Power Supply, J. F. Streib, 
D. Feldman, and W. E. Armstrong, Memorandum 
Report 29-P, Apr. 30, 1943. Div. 4-232.2-M5 

18. Small G. E. Photocells Received May 22, 1943, W. E. 
Williams, Jr., Memorandum Report 34-P, June 7, 1943. 

Div. 4-231. 5-M 16 

19. Frequency Characteristics of Variations of MC-380 
Amplifier, R. Stair, Seymour Golden, and Paul Miller, 
Report OD-2-1 , June 8, 1943. Div. 4-238.221-M3 

20. Matching Photocells and Non-Linear Load Resistors 
in the MC-380 Circuit, J. G. Hoffman and R. F. 
Morrison, Memorandum Report 32-P, June 8, 1943. 

Div. 4-238.41-M4 

21. Spectral Response of Types GL-516 and GL-564 


CONFIDENTIAL 


BIBLIOGRAPHY 


103 


General Electric Photocells, R. Stair and W. E. 
Williams, Jr., Report OD^2-5, June 19, 1943. 

Div. 4-231. 5-M 18 

22. Light Level Values for the North Sky, R. Stair and 
W. E. Williams, Jr., Report OD-2-12, July 3, 1943. 

Div. 4-248-M4 

23. Circuit Parameters Suitable for Use with General 
Electric Pentodes in the MC-380 Unit, R. Stair and 
Seymour Golden, Report OD-2-11, July 8, 1943. 

Div. 4-231. 4-M 11 

24. Sun Firing Properties of M-2 Fuzes, F. L. Mohler, 
Report OD-2-1, July 8, 1943. Div. 4-222.224-M18 

25. Use of the M-2 Fuze, A. V. Astin, Report OD-2-17, 

July 15, 1943. Div. 4-222.224-M20 

26. Progress Report on Double Lenses, F. L. Mohler, 

July 17, 1943. Div. 4-234-M4 

27. Potential Substitutes for Tung Oil and Ceresin Wax, 
P. J. Franklin, Report OD-5-42, July 19, 1943. 

Div. 4-239. 1-M 2 

28. Dielectric Constant and Power Factor Loss of Some 
Potting Materials, P. J. Franklin, Aug. 3, 1943. 

Div. 4-239. 1-M3 

29. Impedance of the MC-380 Input Circuit as a Function 
of Photocell Sensitivity, J. G. Hoffman and R. F. 
Morrison, Report OD-2-16, Aug. 12, 1943. 

Div. 4-238.41-M5 

30. Leakage of Gas into General Electric GL-564 Photo- 

cells, W. E. Williams, Jr., Report OD-2-17, Aug. 28, 
1943. Div. 4-231. 5-M 19 

31. A Sunproof Modification of the MC-380 Fuze, J. G. 

Hoffman, R. F. Morrison, and G. L. Scillian, Report 
OD-2-21, Sept. 4, 1943. Div. 4-247-M4 

32. Results of Tests on 400 R.C.A. Photocells, Type 936, 

Received June 15, 1943, W. E. Williams, Jr., Report 
OD-2-19, Sept. 6, 1943. Div. 4-231. 5-M20 

33. Results of Tests on 2000 G. E. Photocells, Type 1P24, 
Received July 8 and 17, 1943, W. E. Williams, Jr., 
Report OD-2-20, Sept. 7, 1943. Div. 4-231. 5-M21 

34. Revision of the MC-380 Circuit, J. G. Hoffman, R. 
Stair, and A. Orden, Report OD-2-2, Oct. 1, 1943. 

Div. 4-238.1-M2 

35. Laboratory and Field Tests on RPEB-2 Fuze, A. Y. 
Astin and A. Orden, Report OD-2-3, Oct. 23, 1943. 

Div. 4-222 .225-M4 

36. Probability of Sun Firing of M-2 Fuzes, A. V. Astin, 
Report OD-2-4, Nov. 15, 1943. Div. 4-222.224-M25 

37. A Further Study of the Sunproof Modifications of the 
MC-380 Fuze, G. L. Scillian, R. F. Morrison, and 
J. G. Hoffman, Report OD-2-5, Nov. 22, 1943. 

Div. 4-247-M5 

MEMORANDA OF THE ORDNANCE DEVEL- 
OPMENT DIVISION OF THE NATIONAL 
BUREAU OF STANDARDS 

38. Varistor Thyrite Material, R. A. Becker, Mar. 28, 1942. 

Div. 4-236. 1-M 1 

39. Night PE Fuze, J. F. Streib, Apr. 16, 1942. 

Div. 4-248-M 1 

40. Preliminary Test on Night Operation of Photoelectric 
Fuze, ( W.E . Model AR) urith Light Source Carried by 


Projectile, by Means of Falling Spheres, J. F. Streib, 
Apr. 17, 1942. Div. 4-222 .23-MI 

41. Development of Thyrite fox Special Use, R. Hofstadter, 

July 6, 1942. Div. 4-236.1-M2 

42. Photocell-Varistor Combinations, R. Hofstadter and 
R. F. Morrison,' Sept. 9, 1942. Div. 4-238.41-MI 

43. Effect of Variation of Grid Resistor on Initial Input 
Impedance and Performance of One-Stage P.E. Unit, 
R. A. Becker and David Feldman, Sept. 29, 1942. 

Div. 4-236-M 1 

44. Double Input Circuits, J. F. Streib, Nov. 11, 1942. 

Div. 4-238.43-MI 

45. Theoretical Voltage Output from a Double Photocell 
Circuit, R. Hofstadter, Nov. 12, 1942. 

Div. 4-231. 51-M2 

46. Double Lenses, F. L. Mohler, Nov. 13, 1942. 

Div. 4-234-M4 

47. Sun Firing, W. E. Armstrong, Nov. 19, 1942. 

Div. 4-247-M 1 

48. Double Photocell Circuit, T. M. Marion, Dec. 11, 1942. 

Div. 4-231. 51-M3 

49. Operation of Parallel, Double Photocell Circuit, T. M. 

Marion, Dec. 12, 1942. Div. 4-231. 51-M4 

50. Paint Formulation for Methyl Methacrylate Resins, 

P. J. Franklin, Jan. 18, 1943. Div. 4-234.1-MI 

51. Zero Stage Units, R. Hofstadter, Jan. 30, 1943. 

Div. 4-238.42-MI 

52. Zero Stage Units, R. Hofstadter, Feb. 18, 1943. 

Div. 4-238.42-M2 

53. Tube Constants of Pentodes Used in the MC-380 and 
Condenser Unit Circuits, D. Feldman, Feb. 26, 1943. 

Div. 4-231. 4-M8 

54. Uniformity of Fuzes Measured with Half the Lens 
Uniformly Illuminated, F. L. Mohler, Mar. 6, 1943. 

Div. 4-222 .224-M6 

55. Shift in Frequency Transmissions of MC-380, S. Gol- 
den, Mar. 15, 1943. Div. 4-238.1-MI 

56. Photothyratrons, R. F. Morrison, Jr., Mar. 17, 1943. 

Div. 4-231. 1-M6 

57. The Use of High Sensitivity Photocells, J. G. Hoffman, 

Mar. 19, 1943. Div. 4-238.4-MI 

58. Gas-Filled R.C.A. 936 Photocells, T. M. Marion, Mar. 

29, 1943. Div. 4-231. 5-M10 

59. The Balanced Double Input Circuit, J. F. Streib, 

Apr. 1, 1943. Div. 4-238.43-M2 

60. Additional Remarks on Series Double Input Circuit, 

J. F. Streib, Apr. 5, 1943. Div. 4-238.43-M3 

61. Paint to Minimize Crazing, P. J. Franklin, Apr. 7, 1943. 

Div. 4-234. 1-M2 

62. Status of Condenser Unit, A. V. Astin, Apr. 12, 1943. 

Div. 4-237-M 1 

63. Recommendation of Non-Crazing Surface Coating for 
Lucite, P. J. Franklin, Apr. 12, 1943. Div. 4-234.1-M3 

64. Status of Reserve Batteries, A. V. Astin, Apr. 17, 1943. 

Div. 4-232. 1-M6 

65. The Use of High Sensitivity Photocells in the MC-380 
Unit, J. G. Hoffman, Apr. 19, 1943. Div. 4-238.4-MI 

66. Results of Electrical and Mechanical Tests on 95 G. E. 

Photocells Received April 14, 1943, W. E. Williams, 
Jr., Apr. 19, 1943. Div. 4-231.5-M12 


CONFIDENTIAL 


104 


BIBLIOGRAPHY 


67. SA-804 Slow Cooling Pentodes , D. Feldman, Apr. 22, 

1943. Div. 4-231.4-M10 

68. Effect oj Light Level on the Threshold of MC-380 
Units, C. Ravitsky, May 10, 1943. Div. 4-222.224-M10 

69. Radium Treatment of Neon Lamps, C. Brunetti, May 

13, 1943. Div. 4-231 .6-M2 

70. High Sensitivity Photocells, A. V. Astin, June 10, 1943. 

Div. 4-231 .5-M17 

71. A Method for Preventing Sunfiring, T. M. Marion, 

July 8, 1943. Div. 4-247-M2 

72. Test of Willard Reserve A Cell, A. Orden, July 29, 

1943. Div. 4-232. 1-M7 

73. Notes of Double PE Cell Input Circuit, J. G. Hoffman, 

Aug. 12, 1943. Div. 4-231. 51-M5 

74. Sun Transients in the MC-380 Amplifier Circuit, R. F. 

Morrison, Jr., Sept. 10, 1943. Div. 4-238.221-M4 

75. RPEB-2’s Fired at Blossom Point on September 9, 
1943, A. Orden, Sept. 11, 1943. Div. 4-222.225-MI 

SPECIFICATIONS OF THE ORDNANCE 
DIVISION OF THE NATIONAL 
BUREAU OF STANDARDS 

76. Manufacturing Specification for 50 Units to be Manu- 

factured by Westinghouse, S. H. Neddermeyer, June 
6, 1942. Div. 4-222.23-M2 

77. Specification for a Powder Train Interrupter and Elec- 

tric Switch for Fuzes for 43 Projectile, W. B. McLean, 
Aug. 31, 1942. Div. 4-238.511-M2 

78. Proposed Specification for Manufacture and Inspection 
of a Battery for Section E, Division A, NDRC, Sept. 

1, 1942. Div. 4-232.1-M3 

79. Test Specifications for Varistors or Thyrite Units, 
Draft 4, Robert Hofstadter, Sept. 29, 1942. 

Div. 4-236.1-M4 

80. Specification for Manufacture and Testing of SA-780A 

Triode, SA-781A Pentode, and SA-782B Thyratron, 
C. Brunetti, Sept. 30, 1942. Div. 4-231-MI 

81. Specification for HY-145-ZT Pentodes for Photoelec- 
tric Proximity Fuzes, R. A. Becker, Sept. 30, 1942. 

Div. 4-231. 4-M5 

82. Proposed Specification for Manufacture and Inspection 
of GY-2 Thyratron Tube, Sept. 30, 1942. 

Div. 4-231. 1-M2 

83. Tentative Test Specification of Photocell RCA 936 
{Formerly C-7063), Draft 5, Sept. 30, 1942. 

Div. 4-231.5-MI 

84. Specification for Manufacture and Testing of a Photo- 

electric Proximity Fuze for Rocket Projectiles, Sept. 
30, 1942. Div. 4-212.2-M3 

85. MC-380 Mechanical Specifications, C. B. Crane, Nov. 

2, 1942. Div. 4-222 .224-MI 

86. Specification for Manufacture and Inspection of 
Microthyratron Tube, Robert Hofstadter, Nov. 6, 1942. 

Div. 4-231. 1-M3 

87. Specifications or Standards for Inspection of BR 
Lenses, F. L. Mohler, Nov. 30, 1942. Div. 4-234-M7 

88. Proposed Specification for Acceptance Gages to be 

Used with M-2 and M-3 Fuze Components, C. B. 
Crane, Dec. 3, 1942. Div. 4-619-MI 


89. Suggested Form of Specifications for Manufacture and 
Inspection of a Neon Tube, Dec. 16, 1942. 

Div. 4-231 .6-MI 

90. Tentative Specification for Field Test Set IE-28, A. S. 

Clarke, Dec. 31, 1942. Div. 4-222.223-M2 

91. Photocell Specifications; Gas Multiplication Ratio, 

J. F. Streib, Mar. 5, 1943. Div. 4-231.5-M6 

92. Photocell Specifications; Tinning Tabs, J. F. Streib, 

Mar. 8, 1943. Div. 4-231. 5-M9 

93. Photocell Specifications; Flat Region on Seat, J. F. 

Streib, Mar. 8, 1943. Div. 4-231.5-M8 

94. Photocell Specifications ; Uniformity, J. F. Streib, Mar. 

8, 1943. Div. 4-231. 5-M7 

95. Specification for Electron Tube NN1; Description: 

Photocell, June 1, 1943. Div. 4-231.5-M15 

REPORTS AND MEMORANDA OF CON- 
TRACTORS OF DIVISION 4, NDRC 

96. PERF Apparatus, Model BR, as Made by Western 

Electric Company, Inc., Hawthorne Works, Chicago, 
111., Specifications for manufacture, X-61637, Issue 1, 
Systems Development Department, Bell Telephone 
Laboratories, Jan. 29, 1942. Div. 4-212.2-MI 

97. Manufacturing Testing Requirements for Parts and 
Assemblies Used in PERF Apparatus, Western Elec- 
tric Company, Model BR (X-61637) ; Specification for 
testing, X61636, Issue 4, Systems Development Depart- 
ment, Bell Telephone Laboratories, Mar. 9, 1942. 

Div. 4-222 .226-MI 

98. Engineering Memorandum of Trip to Bureau of Stand- 
ards and Baltimore Radio Division, August 3 and 4, 
1942, E. K. Clark, Mansfield Works, Westinghouse 
Electric and Manufacturing Company, Aug. 6, 1942. 

Div. 4-210-MI 

99. Memorandum of Meeting in Washington, August 4> 
W. J. Russell, Mansfield Works, Westinghouse Electric 
and Manufacturing Company, Aug. 6, 1942. 

Div. 4-212.3-M1 

100. Request for Permission to Make a Circuit Wiring 
Change in MC-380- A Fuze Head, Case 23236, J. M. 
West, Bell Telephone Laboratories, Oct. 26, 1942. 

Div. 4-238 .22 1-MI 

101. Memorandum for Record, Case 23826, W. O. Baker, 
Bell Telephone Laboratories, Nov. 27, 1942. 

Div. 4-234-M5 

102. Memorandum for Record, Case 23854, W. O. Baker, 

J. H. Heiss, Jr., and N. R. Pape, Bell Telephone Labo- 
ratories, Nov. 28, 1942. Div. 4-234-M6 

103. Report on Special Phototube Investigation in Research 

Laboratory, June 1, 1942-January 31, 1943, S. Dushman, 
Research Laboratory, General Electric Company, Sche- 
nectady, N. Y., Feb. 2, 1943. Div. 4-231. 5-M5 

104. Final Report on Photoelectric Fuzes, submitted by 
the Bell Telephone Laboratories for the Western Elec- 
tric Company, New York, J. F. Wentz, Mar. 1, 1943. 

Div. 4-212.2-M4 

105. Progress in Photo-Tube Work, Interim Report No. 
171, March 2 to April 8, 1943, S. Dushman, OEMsr- 
611, Research Laboratory, General Electric Company, 
Schenectady, N. Y., Apr. 8, 1943. Div. 4-231. 5-M11 


CONFIDENTIAL 


BIBLIOGRAPHY 


105 


106. Weekly Progress Report for Week Ending May 29, 

1943, S. Dushman, OEMsr-611, Research Laboratory, 
General Electric Company, Schenectady, N. Y., May 
29, 1943. Div. 4-231. 5-M 14 

107. Proximity Fuzes, J. F. Wentz, final report submitted 

by the Bell Telephone Laboratories for the Western 
Electric Company, New York, under Contract OEMsr- 
500. July 31, 1943. Div. 4-212.2-M5 

108. Final Technical Report on Generator-Powered Proxim- 

ity Fuzes for Bombs, report submitted by the Bell 
Telephone Laboratories under Contract OEMsr-905, 
Mar. 24, 1944. Div. 4-211.21-M5 

109. Report to Division 4, National Defense Research 
Committee on Contract OEMsr-1003, A. M. Glover 
and A. R. Moore, Report 1003-1, Radio Corporation 
of America, Lancaster, Pa., Oct. 23, 1944. 

Div. 4-23 1-M3 

U. S. ARMY PUBLICATIONS 

110. Nose MC-380-( ). Specification No. 371-2031, Camp 
Evans Signal Laboratory, Camp Evans, Belmar, N. J., 
Jan. 27, 1943. 

111. Proof Firing Test Formula for Specification Nos. 
371-2027 and 371-2031, Feb. 24, 1943. 

112. TM 11-2502. Test Equipment IE-28, War Department 
Technical Manual, Aug. 31, 1943. 

113. TB 9X-94- Fuze, Rocket, P.D., T4 and T5, War De- 
partment Training Bulletin, Dec. 1944. 

UNCLASSIFIED PUBLICATIONS 

114. Varistors. A group of articles reprinted from Bell 
Laboratories Record. 

115. Thyrite: A G.E. Resistance Material, General Electric 
Company. 


Chapter 6 

ARMOR AND ORDNANCE REPORTS OF 
DIVISION 4 , NDRC 

1. The Photoelectric Proximity Fuze, L. R. Hafstad et al., 

NDRC Report A-20, Part I (Continued), Section 19. 
Oct. 20, 1941, pp. 206-208. Div. 4-212.1-MI 

REPORTS OF THE ORDNANCE DEVELOP- 
MENT DIVISION OF THE NATIONAL 
BUREAU OF STANDARDS 

2. The Photoelectric Proximity Fuze for Rocket Projec- 

tiles, S. H. Neddermeyer, unpublished report, Vol. 2, 
Section 7, pp. 10&-118. Div. 4-212.2-M6 

2a. Ibid., p. 108. 

3. Preliminary Proposal for a System of Matching Non- 

Linear Load Resistors to Photocell, J. G. Hoffman, 
Report 25-P, Apr. 20, 1943. Div. 4-238.41-M2 

4. Proposed Method of Matching Non-Linear Load Re- 

sistors to Photocell, J. G. Hoffman, Report 27-P, May 
4, 1943. Div. 4-238.4 1-M3 


MEMORANDA OF THE ORDNANCE DEVEL- 
OPMENT DIVISION OF THE NATIONAL 
BUREAU OF STANDARDS 

5. Description of Photocell Testing Apparatus and Pro- 

cedure, Memorandum to S. H. Neddermeyer from 
J. F. Streib, Mar. 26, 1942. Div. 4-238.44-MI 

6. Gas Currents and Input Impedance of HY-145-YT, 

Memorandum to J. E. Henderson from R. A. Becker, 
Aug. 1, 1942. Div. 4-231.4-M2 

7. Report on Light Measurements Made on the Altitude 

Flights of August 23 and 28, 1942, J. G. Hoffman, Aug. 
28, 1942. Div. 4-248-M2 

8. Resolving Power of Westinghouse Lenses and Position 
of Photocell; Effective Aperture, Memorandum to 
J. E. Henderson from F. L. Mohler, Sept. 11, 1942. 

Div. 4-234-MI 

9. Varistor Behavior at Different Temperatures, Memo- 

randum to J. E. Henderson from R. Hofstadter, W. C. 
Armstrong, J. Heyman, and R. F. Morrison, Sept. 14, 
1942. Div. 4-236.1-M3 

10. Inspection of Lenses, etc., Memorandum to J. E. 
Henderson from F. L. Mohler, Sept. 18, 1942. 

Div. 4-234-M2 

11. Suggested Procedure for Measuring Photocell Current 
in Testing Sensitivity of the Optical-Photocell System 
of PE Fuze without Disassembling, Memorandum to 
F. L. Mohler from J. F. Streib, Sept. 26, 1942. 

Div. 4-238.44-M2 

12. Effect of Variation of Grid Resistor on Initial Input 

Impedance and Performance of One-Stage PE Unit, 
Memorandum to J. E. Henderson from R. A. Becker 
and D. Feldman, Sept. 29, 1942. Div. 4-236-MI 

13. A Rectified AC Method of Measuring Photocell Char- 

acteristics and Tests on Some Westinghouse Lenses, 
Memorandum to J. E. Henderson from F. L. Mohler, 
Oct. 12, 1942. Div. 4-238.44-M3 

14. Recommendations for Quality Inspection of Lenses in 
the Manufacturing Plant, F. L. Mohler, Oct. 20, 1942. 

Div. 4-234-M3 

15. Photocell Inspection, Memorandum to J. E. Henderson 
from J. F. Streib, Oct. 22, 1942. Div. 4-238.44-M4 

16. Input Impedances of Hytron 145-ZT Pentodes, Memo- 

randum to R. A. Becker from D. Feldman, Nov. 16, 
1942. Div. 4-231. 4-M6 

17. Humidity Tests on Varistor Specifications, Memoran- 
dum to A. Ellett from R. Hofstadter, Nov. 17, 1942. 

Div. 4-236.1-M5 

18. Testing of HY-145-ZT Pentodes, Nov. 27, 1942. 

Div. 4-231. 4-M7 

19. Twenty -Four Hour Humidity Test on Thyrite Units 

and Varistors, Memorandum to R. Hofstadter from 
R. F. Morrison, Dec. 2, 1942. Div. 4-236.1-M6 

20 . Results of Tests on 44 G.E. Photocells to Determine 

the Effect of Change of Illumination on Sensitivity, 
Memorandum to J. E. Henderson and J. F. Streib from 
W. E. Williams, Jan. 7, 1943. Div. 4-231.5-M2 

21. Results of Tests on 30 GE. Photocells to Determine 
the Effect of Change of Illumination on Sensitivity, 


106 


BIBLIOGRAPHY 


Memorandum to J. E. Henderson and J. F. Streib 
from W. E. Williams, Jan. 9, 1943. Div. 4-231.5-M3 

22. Repeated Surges of Thyratrons , Memorandum to J. E. 
Henderson from R. F. Morrison, Feb. 24, 1943. 

Div. 4-231. 1-M5 

23. Measurement of Light Thresholds of MC-380 PE 
Units, Memorandum to J. E. Henderson from S. H. 
Neddermeyer, Mar. 13, 1943. Div. 4-222.224-M7 

24. Preliminary Proposal for a System of Matching Non- 
Linear Load Resistor to Photocell , Memorandum to 
J. G. Hoffman from R. F. Morrison, Apr. 12, 1943. 

25. Matching Photocells and Non-Linear Load Resistors 
in the MC-380 Circuit, Memorandum to A. V. Astin 
from J. G. Hoffman, May 3, 1943. 

26. Matching Photocells and Non-Linear Load Resistors 
in the MC-380 Circuit, Memorandum to A. V. Astin 
from J. G. Hoffman, June 8, 1943. Div. 4-238.41-M4 

27. A Preliminary Report on Sun Firing of the 380 Fuze 
as Measured on the Yaw Machine, Memorandum to 
A. V. Astin from F. L. Mohler, July 8, 1943. 

Div. 4-222 ,224-M 19 

SPECIFICATIONS 

28. Specifications for the HY-145-ZT Pentodes for Photo- 

electric Proximity Fuze, Section E, Division A, NDRC. 
Sept. 30, 1942. Div. 4-231. 4-M5 

29. Specifications for Electron Tube NN1: Description; 

Photocell, June 1, 1943. Div. 4-231 .5-M15 

DRAWINGS OF THE ORDNANCE DEVELOP- 
MENT DIVISION OF THE NATIONAL 
BUREAU OF STANDARDS 

30. NBS Drawing No. 3012: Standard PEC Mount. 

Div. 4-231. 52-MI 

31. NBS Drawing No. 3013: Shutter and Baffle. 

Div. 4-231. 52-M2 

32. NBS Drawing No. 3014: Test Cell Mount Assembly. 

Div. 4-231 52-M3 

33. NBS Drawing No. 3015: Test Cell Mount Details. 

Div. 4-231. 52-M4 

34. NBS Drawing No. 3016: Test Cell Mount Details. 

Div. 4-231. 52-M4 

35. NBS Drawing No. 3017 : Lamp Socket. 

Div. 4-231. 52-M5 

36. NBS Drawing No. 3018: PEC Test Unit Cabinet. 

Div. 4-231. 52-M6 

37. NBS Drawing No. 3019: PEC Test Unit Cabinet. 

Div. 4-231. 52-M7 

38. NBS Drawing No. A3164: Light Angle Device Wiring 

Diagram. Div. 4-231. 52-M8 

39. NBS Drawing No. L5017 : Photocell. 

Div. 4-231.5-M13 

Chapter 7 

ARMOR AND ORDNANCE REPORTS OF 
DIVISION 4, NDRC 


la. Ibid., pp. 275-306. 

lb. Ibid., pp. 307-355. 

2. Radio Reporters for Proximity Fuze Testing, A. V. 
Astin, NDRC Report A-53, May 21, 1942. 

Div. 4-61 1-MI 

REPORTS OF THE ORDNANCE DEVELOP- 
MENT DIVISION OF THE NATIONAL 
BUREAU OF STANDARDS 

3. The Photoelectric Proximity Fuze for Rocket Pro- 

jectiles, S. H. Neddermeyer, unpublished report, Vol. 
2, Section 8, pp. 119-132. Div. 4-212.2-M6 

4. Analysis of Proving Ground Data on Experimental 
Photoelectric Fuzes Fired at Fort Fisher, unpublished 
report. 

5. PE Range Testing at Corncake with Reporters, A. V. 
Astin, Memorandum Report P. G. 209, Aug. 21, 1942. 

Div. 4-222 .22 1-M2 

6. PE Range Tests with Radio Reporters, A. V. Astin, 
Memorandum Report P. G. 244, Sept. 1, 1942. 

Div. 4-222 .22 1-M3 

7. PE Range Tests with Reporters, A. V. Astin, Memo- 
randum Report P. G. 303, Sept. 25, 1942. 

Div. 4-222 .221-M4 

8. Photocell Current Measurements with Reporters, A. 

V. Astin, Memorandum Report P. G. 305, Sept. 26, 
1942. Div. 4-222 .22 1-M5 

9. Proposed Proof Range for M-2 and M-3 Fuzes at 

Aberdeen Proving Center, H. Diamond, Memorandum 
Report 1-M, Dec. 29, 1942. Div. 4-222.223-MI 

10. Range Testing at Blossom Point for PE Fuzes, A. V. 

Astin, Report 14-T, Jan. 5, 1943. 

Div. 4-222 .224-M4 

11. Yaw Reporter Test, L. C. Miller, Report 401-T, 

Aug. 9, 1943. Div. 4-222 .221-M7 

12. Laboratory and Field Tests on RPEB-2 Fuze, A. V. 
Astin and A. Orden, Report OD-2-3, Oct. 23, 1943. 

Div. 4-222 .225-M4 

13. Report of Tests with Reporters at Aberdeen, Memo- 
randum from A. V. Astin, Nov. 29, 1941. 

Div. 4-222 .221-MI 

14. Range Firing of Radio Reporters and PE Fuzes to 
Determine Suitability of Range for Testing PE Fuzes 
at Blossom Point, Md., Memorandum to J. E. Hender- 
son from J. F. Streib, Dec. 16, 1942. 

Div. 4-222 .221-M6 

15. Targets for MC-380 Units, Memorandum to H. 
Diamond from A. Y. Astin, July 3, 1943. 

Div. 4-618-M3 


Chapter 8 

ARMOR AND ORDNANCE REPORTS OF 
DIVISION 4, NDRC 


1. The Photoelectric Proximity Fuze, L. R. Hafstad et al., 
NDRC Report A-20, Part I (Continued), Oct. 20, 1941. 

Div. 4-212. 1-M 1 


1. The Photoelectric Proximity Fuze, L. R. Hafstad et al., 
NDRC Report A-20, Part I (Continued), Section 28, 
Oct. 20, 1941. Div. 4-212.1-MI 


CONFIDENTIAL 


BIBLIOGRAPHY 


107 


REPORTS OF THE ORDNANCE DEVELOP- 
MENT DIVISION OF THE NATIONAL 
BUREAU OF STANDARDS 

2. The Photoelectric Proximity Fuze for Rocket Pro- 

jectiles, S. H. Neddermeyer, unpublished report, 
Volume 1. Div. 4-212.2-M6 

3. PE Fuzes for 4% PP Rocket, Condenser B Supply, 

Report on Target Function, 12 Rounds, Corncake, 
December 31, 1942, T. N. White, Report 19-T, Jan. 
12, 1943. Div. 4-222 .222-M2 

4. Frequency of Yaw of Budd 4%-inch Rockets Fired 
from a Plane, T. B. Godfrey, Report 47-T, Feb. 11, 
1943. 

5. Fuze, Rocket, PED Condenser-Powered Westinghouse, 
N Range, Corncake, March 4 and 5, 1943, R. Vorkink, 
Report 108-T, Mar. 23, 1943. Div. 4-222.222-M4 

6. Range Test at Blossom Point with PEP Rocket Fuzes, 
L. C. Miller, Report 116-T, Mar. 24, 1943. 

Div. 4-222.222-M5 

7. Fuze MC-380 Wurlitzer, Rejects with Changed Cou- 

pling Condensers, Target Function Test, T. N. White, 
Report 155-T, Apr. 12, 1943 Div. 4-618-MI 

8. Fuze MC-380 B (Westinghouse) with Pentode Plate 

and Screen Resistor Changes, L. C. Miller, Report 
167-T, Apr. 20, 1943. Div. 4-222.224-M8 

9. Evaluations of Ground-Approach Functions, PEP and 
RRP Fuzes, Fort Bragg, April 14 and 15, 1943, J. L. 
Thomas and T. N. White, Report 180-T, Apr. 23, 1943. 

Div. 4-241-MI 

10. Test of Special MC-380 Fuzes — Westinghouse in Con- 
nection with the Problem of Gassy Pentodes, L. C. 
Miller, Report 232-T, May 10, 1943. 

Div. 4-222 .224-M 11 

11. Test of Special MC-380 Western Electric Fuzes 

(Veazie Circuit) in Connection with the Problem of 
Gassy Pentodes, L. C. Miller, Report 244-T, May 19, 
1943. Div. 4-222 .224-M 12 

12. Test of Special MC-380 Western Electric Fuzes in 
Connection with the Problem of Gassy Pentodes, 
L. C. Miller, Report 271-T, June 3, 1943. 

Div. 4-222 .224-M 13 

13. Experimental MC-380 Fuzes Fired against Small 

Flat Target, North Range, Corncake, May 27, 28, 29, 
30, 1943, T. N. White and A. V. Astin, Report 337-T, 
July 7, 1943. Div. 4-222.224-M17 

14. Fuze PEP-M-2, MC-380-NBS Special Modified Fuzes, 

Test for Target Function, R. Vorkink, Report 346-T, 
July 5, 1943. Div. 4-618-M4 

15. Fuze PEP-M-2, MC-380-NBS Special Rejects, Test 

for Target Function, R. Vorkink, Report 347-T, July 
6, 1943. Div. 4-618-M5 

16. Fuze PEP-M-2, MC-380-Westinghouse Special Micro- 
phonic Rejects, R. Vorkink, Report 348-T, July 7, 1943. 

Div. 4-222 .226-M2 

17. Test on Microphonic MC-380 Fuzes, D. C. Friedman, 

Report 378-T, July 22, 1943. Div. 4-222.224-M21 

18. Test of Five BTL BP EG Fuzes, L. C. Miller, Report 

387-T, July 24, 1943. Div. 4-222.21-M2 

19. Sun Firing of Photoelectric Fuzes on Rockets, H. F. 
Stimson, Report 392-T, Sept. 3, 1943. 

Div. 4-247-M3 


20. Yaw Reporter Test, L. C. Miller, Report 401-T, Aug. 

9, 1943. Div. 4-222.221-M7 

21. Ten BTL BPEG Fuzes, Tests for Target Functions 

and Self-Destruction, R. Vorkink, Report 410-T, Aug. 
12, 1943. Div. 4-222 .2 1-M3 

22. Test of Special MC-380 Fuzes Designed to Prevent 
Sunfiring, L. C. Miller, Report 428-T, Sept. 4, 1943. 

Div. 4-222 .224-M23 

23. Analysis of Field Tests of Condenser-Powered PE 
Units, Fort Fisher, March 3, 4, and 5, 1943, S. H. 
Neddermeyer, Report 16-P, Mar. 6, 1943. 

Div. 4-222 .222-M3 

24. Tests of Photoelectric Fuzes on Rotating 4^-inch 

Budd Rockets, March 1, 1943, S. H. Neddermeyer, 
Report 17-P, Mar. 26, 1943. Div. 4-222.23-M4 

25. Uniformity of MC-380 Fuze Noses Measured with 

Half the Lens Uniformly Illuminated, F. L. Mohler, 
Report 18-P, Mar. 26, 1943. Div. 4-222 .224-M6 

26. Ground Firing Tests of MC-380 Fuzes at Fort Bragg, 

April 14-15, 1943, A. V. Astin, Report 22-P, Apr. 22, 
1943. Div. 4-222 .224-M 9 

27. Test of Bomb Mounted MC-380 Fuzes at Aberdeen, 
A. V. Astin, Report 23-P, Apr. 23, 1943. 

Div. 4-222 .2 1-MI 

28. Tests of MC-380 Units with Photocells Rejected for 

Excessive Fragments, A. V. Astin and W. E. Williams, 
Report 38-P, June 29, 1943. Div. 4-222.224-M15 

29. Triggering of MC-380’ s by Poles on the North Range, 
A. Orden, Report 39-P, July 3, 1943. 

Div. 4-222 .224-M 16 

30. Use of MC-380’s on AN-M-30 at Eglin Field, July 26 

through July 30, 1943, A. V. Astin, Report 42-P, 
Aug. 5, 1943. Div. 4-222.224-M22 

31. Target Test of 67 RPEB-2 Fuzes with 20 MC-380 
Controls (Using 4 Target Array), at Blossom Point, 
R. Vorkink, Report OD-1-9, Sept. 20, 1943. 

Div. 4-222. 225-M2 

32. Salvo Firing in Search of Sympathetic Functioning , 

F. R. Kotter and T. N. White, Report OD-1-15, 
Sept. 25, 1943. Div. 4-245-MI 

33. Target Test of 79 RPEB with 30 MC-380 Controls 
Using 4 Target Array at Blossom Point, R. Vorkink, 
Report OD-1-25, Oct. 14, 1943. Div. 4-222 .225-M3 

34. Test of 25 Sun-Proofed MC-380 Fuzes with 50 Regular 
MC-380 Controls, Fired over Ground, R. Vorkink, 
Report OD-1-36, Nov. 8, 1943. Div. 4-222.224-M24 

35. Effect of Rocket Spin upon the Performance of VT 
Fuzes, T-4, T-5, T-6, T. B. Godfrey, Report OD-1- 
668, Mar. 13, 1945. 

36. Sun Firing Properties of M-2 Fuzes: I. Roof Tests on 

Yaw Machines; II. Field Tests at Corncake June 1 
and June 7, 1943, F. L. Mohler, Report OD-2-1, July 
8, 1943. Div. 4-222. 224-M 18 

37. Revision of the MC-380 Circuit, J. G. Hoffman, R. 
Stair, and A. Orden, Report OD-2-2, Oct. 1, 1943. 

Div. 4-238.1-M2 

38. Laboratory and Field Tests on RPEB-2 Fuze, A. V. 
Astin and A. Orden, Report OD-2-3, Oct. 23, 1943. 

Div. 4-222.225-M4 

39. Probability of Sun Firing of M-2 Fuzes, A. V. Astin, 
Report OD-2-4, Nov. 15, 1943. Div. 4-222.224-M25 


CONFIDENTIAL 


108 


BIBLIOGRAPHY 


40. A Further Study of the Sun-Proof Modification of the 
MC-380 Fuze, G. L. Scillian, R. F. Morrison, and 
J. G. Hoffman, Report OD-2-5, Nov. 22. 1943. 

Div. 4-247-M5 

41. Correlation of Laboratory and Field Tests of MC-380 
Microphonic Rejects, A. V. Astin and P. J. Franklin, 
Report OD-2-9, June 28, 1943. Div. 4-222 ,224-M 14 

42. A Sun-Proof Modification of the MC-380 Fuze, J. G. 

Hoffman, R. F. Morrison, and G. L. Scillian, Report 
OD-2-21 . Sept. 4. 1943. Div.4-247-M4 

MEMORANDA OF THE ORDNANCE DEVELOP- 
MENT DIVISION OF THE NATIONAL 
BUREAU OF STANDARDS 

43. Regarding Zero Stage Units, Memorandum to J. E. 
Henderson from R. Hofstadter, Aug. 1, 1942. 

Div. 4-238.42-MI 

44. Firing PE Fuzes, Fort Fisher, August 6-9, 1942, Kite 

Target, North Range; Zero Stage Units; Ground 
Target on Beach; Radio Range, Memorandum to J. E. 
Henderson from R. Hofstadter and J. F. Streib. Aug. 
12, 1942. Div. 4-222 .23-M3 

45. Progress Report No. 2 on Condenser Driven Single- 
Stage PE Unit, Memorandum to J. E. Henderson from 
C. Ravitsky and D. Feldman, Dec. 14. 1942. 

Div.4-212.3-M2 

46. Acceptance Tests of Westinghouse Ml, Sii-inch 

Rockets, Carrying Ml PE Fuzes at Aberdeen, Memo- 
randum to H. Diamond from L. S. Taylor. 425. Dec. 
15, 1942. Div. 4-413-M3 

47. Report on Proving Ground Test of 12 Condenser- 

Powered PE Units Fired on the North Range, Fort 
Fisher, December 31, 1942, Memorandum to J. E. 
Henderson from R. A. Becker and D. Feldman, Jan. 
2, 1943. Div. 4-222 ,222-Ml 

48. Zero Stage Units, Memorandum to J. E. Henderson 
from R. Hofstadter and R. F. Morrison, Jan. 30. 1943. 

49. Status of Condenser Unit, Memorandum to H. Dia- 
mond from A. V. Astin, Apr. 12, 1943. Div. 4-237-MI 

50. Trips to Aberdeen to Observe the Firing of PE and 

Radio Fuzes on Motors Loaded with HE, Memo- 
randum to A. Y. Astin from F. L. Mohler, May 25. 
1943. Div. 4-222.23-M6 

51. Further Observations on the Firing of M-2 and M-3 
Fuzes on M-8 Projectiles at Aberdeen, Memorandum 
to H. Diamond from T. B. Godfrey, May 25. 1943. 

Div. 4-222.223-M3 

52. Targets for MC-380 Units, Memorandum to H. Dia- 
mond from A. V. Astin, July 3, 1943. Div.4-618-M3 

Chapter 9 

1. Rocket Targets as of November 1, 1941, NDRC Report 
A-27, A. J. Dempster, Dec. 24, 1941. Div. 4-412.4-MI 

2. Rocket Flight Tests at Aberdeen, NBS Report PG-48, 

Feb. 5, 1942. Div.4-413-Ml 

3. Flight Tests on 325-in. Rockets, NBS Report PG- 

87, May 16, 1942. Div.4-413-M2 

4. Tests of Miscellaneous Rocket Motors, May 31, 1942, 
NBS Report PG-97, May 31. 1942. Div. 4-411. 1-M3 

5. Preliminary Report on Tests of Cenco Rocket Motors 
Received June 12, 1942, NBS Report PG-106. 

Div. 4-41 1.1-M4 

6. NBS Drawing 440 R. 

Div. 4-411. 1-MI or Div. 4-411.1-M2 

7. NBS 11-5 Drawings A-30686, A-30688, and A-30697 . 

Div.4-411.3-Ml 

8. NBS 11-5 Specification 1934- 

9. NBS Drawings A-448, 443, 444, 447. Div. 4-411.2-MI 

10. Field Test, Ballistics of T-25 Mortar Shells ( MX-24 ), 

Blossom Point, October 29, 30, 31 and November 2, 


1945, G. Rabinow, Report OD-1-901, Nov. 29, 1945. 

Div. 4-51 1-M2 

11. Preliminary Ballistic Measurements on Mortar Shell, 

M43A1, Using Different Types of Fuzes, L. M. Andrews, 
Report OD-4-46, Apr. 15, 1944. Also Supplement to 
OD-4-46, June 5, 1944. Div.4-514-Ml 

12. Wind Tunnel Tests on MRLG Units, L. M. Andrews, 

Report OD-4-76, July 24, 1944. Div.4-514-M2 

13. Summary of Wind Tunnel Ballistics of MRLG and 

MROG Fuzes on M43A1 Shells, L. M. Andrews, Re- 
port OD-4-102, Apr. 2, 1945. Div.4-513-Ml 

14. Suggestion for the New 81-mm Mortar Shell, L. M. 
Andrews, J. Rabinow, Report OD-4-103, Aug. 25. 1945. 

Div. 4-513-M2 

15. Ballistic Data on the T-25, Mortar Shell, L. M. 

Andrews, Report OD-4-103, Supplement 1, Aug. 25, 
1945. Div. 4-51 1-MI 

16. Effect of a Lighter Weight Fin Assembly on Stability 

of the M-56 and T-25 Mortar Shells, L. M. Andrews, 
O. R. Cruzen, Report OD-4-103, Supplement 2, Nov. 
21, 1945. Div. 4-513-M3 

17. Effect of Fin Shape on T-25 Mortar Ballistics, L. M. 

Andrews, Report OD-4-103, Supplement 3, Dec. 17, 
1945. Div. 4-513-M4 

18. T-25 Ballistic Data, L. M. Andrews, Report OD-4-103, 

Supplement 4, Jan. 23, 1946. Div.4-511-M4 

19. Physical Tests on T-25 Shell Sections, L. Schuman, 
Report OD-4-103, Supplement 5, Dec. 26, 1945. 

Div. 4-51 1-M3, 

20. The Magnetic Field Machine, Jesse W. M. du Mond, 
NDRC Report A-8, p. 145, Figures 28, 29. 

21. Letter (Re4a2) from Admiral W. H. P. Blandy to Dr. 
A. Ellett, Feb. 24, 1942. 

22. Radar Ranging on Anti-Aircraft Shell Bursts as of 
May 1, 1942, NDRC Report A-68, R. D. Huntoon. 

23. Memorandum to H. Diamond, Aug. 29. 1942, from 
R. D. Huntoon. 

24. Report of A.A. Board on Project 22. “Radar Shell 
Burst Ranging,” Sept. 23. 1942. 

25. NDRC Report WA-33-2; report of J. Lawson. 

26. NDRC Report WA-71-14; equipment GL3(X). 

27. Intelligence Report, Serial 920, Naval Attache at Lon- 
don, May 20, 1941. 

28. Intelligence Report, Serial 213, Naval Attache at Lon- 
don, Feb. 11, 1941. 

29. ONI Report, Serial 256, N.A.A. London, Jan. 29, 1942. 

30. BuOrd Letter S67(Re4al), Dec. 19. 1941. 

31. C.O. R.O.E. Letter DD418/S67/A5, Serial 01. Jan. 5, 
1942. 

32. Letter from Navy Department to Dr. R. C. Tolman, 
File No .(SC)S78-l(SONRD),Oct.24,1941. Div.4-730-M2 

33. Memorandum on Radar Ranging — Tests at Parris 
Island, S67G047) Re4, Oct. 13, 1941. Div. 4-730-MI 

34. Serial 920 N.A.A. London, May 20, 1941. 

35. NDRC Report W-143-1, Section f. 

36. The Aerodynamics of Controlled-Trajectory Bombs, 
H. L. Dryden, NDRC Report A-32, February 1942. 

Div. 4-242.1 1-MI 

37. Controlled-Trajectory Bombs as of March 1, 1942, 

H. L. Dryden, March 1942. Div. 4-242.1 1-M2 

38. The State of Development of Maneuverable Con- 

trolled-Trajectory Bombs, as of September 1, 1942, 
H. L. Dryden, October 1942. Div. 4-242.1 1-M3 

39. Treatments and Tests for Cotton Fabrics for Powder 

Bags, Ralph T. Mease, NDRC Report A-72, July 
1942. Div. 4-710-M3 

40. Development of Substitutes for Silk in Powder Bags, 

Ralph T. Mease, NDRC Report A-32M. January 
1942. Div. 4-710-MI 

41. Effect of Oxides of Nitrogen on Fabrics, Ralph T. 
Mease, NDRC Report A-35M,June 1942. Div. 4-710-M2 


CONFIDENTIAL 


OSRD APPOINTEES 


division 4 
Chief 

Alexander Ellett 


Technical Aides 


A. S. Clarke 


John S. Rinehart 

Sebastian Karrer 


E. R. Shaeffer 

Cathryn Pike 

R. M. Zabel 

Members 

A. G. Thomas 

L. J. Briggs 


Harry Diamond 

W. D. COOLIDGE 

J. L. Tate 

Special Assistants 

F. L. Hovde 

M. G. Domsitz 


Joseph Kaufman 

W. E. Elliott 


J. L. Thomas 

Wendell Gould 


E. A. Turner 

W. S. Hinman, Jr. 

Consultants 

F. C. Wood 

A. V. Astin 


D. H. Loughridge 

R. A. Becker 


W. B. McLean 

R. M. Bowie 


F. L. Mohler 

Cledo Brunetti 


S. H. Neddermeyer 

J. W. DuMond 


H. F. Olsen 

Saul Dushman 


C. H. Page 

Wm. Fondiller 


W. J. Shackelton 

T. B. Godfrey 


F. B. SlLSBEE 

L. R. Hafstad 


K. D. Smith 

J. E. Henderson 


G. W. Stewart 

R. D. Huntoon 


J. F. Streib 

J. A. Jacobs 


L. S. Taylor 

R. B. Janes 


G. W. VlNAL 

T. Lauritsen 


W. L. Whitson 


R. M. Zabel 


CONFIDENTIAL 


L 


109 


CONTRACT NUMBERS, CONTRACTORS, AND SUBJECTS OF CONTRACTS 


The National Bureau of Standards, which served as the central labora- 
tories for Division 4, NDRC, did not operate under a contract but 
as a government agency under a direct transfer of funds from OSRD. 


Contract 

Number 

Name and Address of Contractor 

Subject 

NDCrc-170 

^DCrc-195 

Western Electric Company 

New York, New York 

Studies and experimental investigations in connection with the 
development of photoelectric devices. 

Western Electric Company 

New York, New York 

Studies and experimental investigations for the development 
of a magnetic instrument. 

OEMsr-76 

Western Electric Company 

New York, New York 

Purchase of 200 photoelectric units. 

OEMsr-99 

General Electric Company 

Schenectady, New York 

Studies and investigations on continuously adjustable time 
fuzes and associated equipment. 

OEMsr-141 

Radio Corporation of America 

Camden, New Jersey 

Development and delivery of remote control equipment for 
aerial torpedoes. 

OEMsr-145 

Western Electric Company 

New York, New York 

Studies and experimental investigation in connection with the 
development on photoelectric devices. 

OEMsr-171 

Radio Corporation of America 

Camden, New Jersey 

Studies and experimental investigations for the development 
of television pickup units of improved sensitivity and report 
the results thereof. 

NDCrc-173 

Radio Corporation of America 

Circuit development of new pickup tube. 

OEMsr-255 

Western Electric Company 

New York, New York 

Studies and experimental investigations in connection with 
photoelectric devices. 

OEMsr-258 

Bendix Aviation Corporation 

Baltimore, Maryland 

Studies and experimental investigations in connection with 
continuous development work on special radio devices. 

OEMsr-298 

Radio Corporation of America 

Camden, New Jersey 

Supply certain television and related equipment. 

OEMsr-343 

Westinghouse Electric and Manufacturing 
Company 

Baltimore, Maryland 

Studies and experimental investigations in connection with the 
development of special radio devices. 

OEMsr-441 

Radio Corporation of America 

Camden, New Jersey 

Studies and experimental investigations in connection with the 
development of special electronic circuits and equipments. 

OEMsr-476 

Vidal Aircraft Company, Inc. 

Camden, New Jersey 

Redesign and construction of gliders. 

OEMsr-500 

Western Electric Company 

New York, New York 

Studies and experimental investigations in connection with the 
development of electronic devices. 

OEMsr-501 

Western Electric Company 

New York, New York 

Purchase of 200 photoelectric units and 1,000 hytron tubes. 

OEMsr-513 

Radio Corporation of America 

Camden, New Jersey 

Development of compact frequency modulation television 
equipment. 

OEMsr-514 

Radio Corporation of America 

Camden, New Jersey 

Development of a new television jamming technique. 

OEMsr-515 

Radio Corporation of America 

Camden, New Jersey 

Development of a more sensitive television pickup unit. 

OEMsr-528 

National Carbon Company 

New York, New York 

Production of small batteries suitable for operation at low 
temperatures. 

OEMsr-566 

Raytheon Production Corp. 

Newton, Massachusetts 

Studies and experimental investigations in connection with the 
development of miniature vacuum tubes. 

110 

CONFIDENT! AL 


CONTRACT NUMBERS, CONTRACTORS, AND SUBJECTS OF CONTRACTS ( Continued ) 


Contract 

Number Name and Address of Contractor Subject 


Studies and experimental investigations in connection with the 
development of miniature vacuum tubes, and report the 
results thereof. 


OEMsr-611 

General Electric Company 

Schenectady, New York 

OEMsr-630 

Sylvania Electric Products 

Salem, Massachusetts 

OEMsr-769 

University of Iowa 

Iowa City, Iowa 

OEMsr-866 

Philco Corporation 

Philadelphia, Pennsylvania 

OEMsr-885 

Emerson Radio and Phonograph 
Corporation 

New York, New York 

OEMsr-887 

Washington Institute of Technology 
Washington, D. C. 

OEMsr-905 

Western Electric Company 

New York, New York 

OEMsr-939 

Westinghouse Electric and Manufacturing 
Company 

Mansfield, Ohio 

OEMsr-941 

Federal Telephone and Radio Corporation 
East Newark, New Jersey 

OEMsr-949 

University of Florida 

Gainesville, Florida 

OEMsr-954 

The Zell Corporation 

Baltimore, Maryland 

OEMsr-980 

Zenith Radio Corporation 

Chicago, Illinois 

OEMsr-981 

Knapp-Monarch Company 

St. Louis, Missouri 

OEMsr-1003 

Radio Corporation of America 

Harrison, New Jersey 

OEMsr-1106 

Westinghouse Electric and Manufacturing 
Company 

Washington, D. C. 

OEMsr-1109 

General Electric Company 

Schenectady, New York 

OEMsr-1113 

Emerson Radio and Phonograph 
Corporation 

. New York, New York 

OEMsr-1117 

Globe-Union, Inc. 

Milwaukee, Wisconsin 

OEMsr-1133 

Zenith Radio Corporation 

Chicago, Illinois 


Studies and experimental investigations in connection with the 
development of miniature vacuum tubes having a very low 
microphonic output. 

Studies and experimental investigations in connection with 
development work on special electronic devices and associ- 
ated equipment. 

Studies and experimental investigations in connection with the 
development of special radio devices and associated equip- 
ment. 

Studies and experimental investigations in connection with and 
carry on continuous development work on special radio de- 
vices and associated equipment. 

Development of accessories for special electronic devices and 
associated equipment. 

Studies and experimental investigations in connection with the 
development of special electronic devices. 

Studies and experimental investigations in connection with the 
development of illumination indicators. 

Studies and experimental investigations in connection with the 
development of special selenium rectifiers. 

Conduct theoretical studies and experimental investigations in 
connection with problems peculiar to special electronic de- 
vices for ordnance application. 

Furnishing machining facilities in connection with development 
of special electronic devices. 

Studies and experimental investigations in connection with 
development of special electronic devices. 

Studies and experimental investigations in connection with 
development of special power supplies and associated equip- 
ment. 

Studies and experimental investigations in connection with 
development of special miniature vacuum tubes. 

Pilot production of special electronic devices. 


Studies and experimental investigations in connection with 
development work on special electrical and radio devices and 
associated equipment. 

Manufacture and delivery of special electronic devices. 


Studies and experimental investigations in connection with 
development of special electrical and mechanical devices. 

Manufacture and delivery of special electronic devices. 


CONFIDENTIAL 


111 


CONTRACT NUMBERS, CONTRACTORS, AND SUBJECTS OF CONTRACTS ( Continued ) 


Contract 

Number 

Name and Address of Contractor 

Subject 

OEMsr-1134 

Knapp-Monarch Company 

St. Louis, Missouri 

Manufacture and delivery of special power supplies. 

OEMsr-1161 

The Rudolph Wurlitzer Co. 

North Tonawanda, New York 

Studies and experimental investigations in connection with the 
development of special electronic devices. 

OEMsr-1163 

The Rudolph Wurlitzer Co. 

North Tonawanda, New York 

Manufacture and delivery of special electronic devices. 

OEMsr-1196 

Philco Corporation 

Philadelphia, Pennsylvania 

Manufacture and delivery of special electronic devices. 

OEMsr-1227 

Bowen and Company, Inc. 

Bethesda, Maryland 

Furnish necessary machine shop and assembly facilities for the 
development of special electronic devices. 

OEMsr-1251 

General Electric Company 

Schenectady, New York 

Manufacture and delivery of special electronic devices. 

OEMsr-1378 

Raymond Engineering Laboratories 
Berlin, Connecticut 

Studies and experimental investigations in connection with the 
development of special electronic devices. 

OEMsr-1417 

The Magnavox Company 

Fort Wayne, Indiana 

Design toss bombing for production. 

OEMsr-1437 

The General Instrument Corp. 

Elizabeth, New Jersey 

Studies and experimental investigations in connection with 
development of electronic and mechanical devices. 

OEMsr-1477 

Zenith Radio Corporation 

Chicago, Illinois 

Development and production of special electronic devices. 

OEMsr-1500 

Emerson Radio and Phonograph 
Corporation 

New York, New York 


OEMsr-1501 

Solar Aircraft, Inc. 

San Diego, California 

Design and produce donut type setback arming devices for use 
on British rockets equipped with VT fuzes. 


112 


CONFIDENTIAL 


SERVICE PROJECT NUMBERS 


The projects listed below were transmitted to the Executive Secretary, 
NDRC, from the War or Navy Department through either the War 
Department Liaison Officer for NDRC or the Office of Research and 
Inventions (formerly the Coordinator of Research and Development), 
Navy Department. 


Service Project Number 


Subject 


Chemical Warfare Service 
CWS-19 

Army Air Forces 

AC-36 

AC-62 


Development of an influence fuze for airplane spray apparatus. 

Controlled-trajectory bombs. 

Development of toss bombing equipment. 


Navy 

NO-5 

NO-111 

NO-115 

NO-183 


Development of substitute materials for silk powder bags. 

Radar ranging on shell bursts. 

Development of a radar homing bomb which homes on a target illuminated by radar, the 
illumination being provided either by the bomb-carrying plane or by other means. 
Development of toss bombing equipment. 


Ordnance Department 

OD-27 

OD-33 

OD-50 

(Transferred to Section T 
April 18, 1942) 

OD-112 

OD-191 

OD-192 


Development of proximity (influence) fuzes for bombs and projectiles. 

Development of a fuze for use in bombardment flares, photoflash bombs, and fragmentation 
bombs. 

Development of the photoelectric type proximity fuze for use on AA shells. 


Development of toss bombing equipment and techniques. 
Development of VT fuze UHF and VHF circuit elements. 
Development of counter-countermeasures for VT fuzes. 


Signal Corps 

SC-38 

SC-40 


Field testing equipment for proximity fuzes. 
Substitute for dry battery BA-55. 


CONFIDENTIAL 


113 



INDEX 


/ 


The subject indexes of all STR volumes are combined in a master index printed in a separate volume. 
For access to the index volume consult the Army or Navy Agency listed on the reverse of the half-title page. 


Aberdeen Proving Ground, 75-76 
Acoustic proximity fuzes, 17-18 
ADP, use in treated cotton fabrics, 99 
Airborne target tests, bomb fuzes, 70 
Airburst fuzes, 12-14 
advantages of air burst, 12-13 
electrostatic, 17 
pressure fuzes, 17 
requirements, 3 

optimum height of burst, 12-13 
types, 13-14 

Ammonium dihydrogen phosphate, for 
treating cotton fabrics, 99 
Antiaircraft fuzes, 17-18 
Antiaircraft training, target rockets, 
90, 91 

launcher, 91 
swaged nozzle, 90 

Applied Mathematics Panel, NDRC, 7 
AR fuze (aircraft rocket), 5 

BA-75, T-4 fuze battery, 40 
Bar-type proximity fuze, 3 
Bell Telephone Laboratories, 96 
Benjamin circuit, British, 14-15 
Blossom Point Proving Ground, 71 
Bomb fuzes, 5-6 
generator-powered, 5, 49, 88 
M-166; 5, 7 
M-168; 5 
T-4 fuze, 87 
T-50 El ; 5 
T-51 ; 5, 7 
T-52; 21, 49, 88 
T-89; 5 
T-91 ; 5-6 
T-91 El; 6 
T-92; 5 

tests, 70-71, 87-88 
Bomb tossing, 8-10 
Bombs, controlled-trajectory, 98-99 
radio link, 98 
television equipment, 98 
BPEG fuze (bomb, PE, generator), 21, 
49, 88 

BR fuze (Mark I), 38 
British 

Benjamin circuit, 14-15 
No. 44 pistol fuze, 17 
UP rocket fuze, 14-15 
Bureau of Standards, 62 

Cartridge bags, use of silk substitutes, 
99 


Cenco motors (experimental rockets), 
89-90 

Cesium-antimony for photocell sur- 
face, 56 

Condenser-powered fuzes, 50-52 
advantages, 86 
circuit, 50 

heater cathode tubes, 50-51 
photothyratons, 51 
reserve batteries, 50 
Controlled-trajectory bombs, 98-99 
radio link, 98 
television equipment, 98 
Cotton substitutes for silk cartridge 
bags, 99 

Doppler-type proximity fuze, 2 

Echo ranging by radar, 97-98 
Electrostatic fuzes, 17 

Fort Bragg, T-4 tests, 75 
Fort Fisher, T-4 tests, 80-81 
Fort Monroe, Virginia, 90 
Fuzes 

see also Photoelectric fuzes 
airburst, 12-14 

bomb fuzes, 5-6, 70-71, 87-88 
classification, 12 
condenser-powered, 50-52, 86 
infrared, 18 
MC-380, 38-40, 76-77 
optical, 18 
pressure, 17 
proximity, 2-8, 16-19 
rocket fuzes, 14-16, 38-49, 70-73, 86- 
87 

T-4; 38-47, 59-69, 77-84 
time fuzes, 14-17 

General Electric Company 
antiaircraft rocket fuze, 14 
photocell, 56, 57 
Generator-powered fuzes 
bomb fuzes, 5, 21, 49, 88 
rocket fuzes, 47-49 
GL-516 photocell, 56 
GL-564 photocell, 56-57 

Hexamethylene tetramine, for treating 
cotton fabrics, 99 

HVAR fuze (high-velocity aircraft 
rocket), 5 


IE 28, test equipment for T-4 fuze, 40 
Infrared fuze, 18 

Japanese photoelectric fuze, 18 

Kewaskum Aluminum Company, OS- 
OS 

Look-forward angle, photoelectric 
fuzes, 24-25 
definition, 24 
model BR, 38 
T-4; 38 

M-8 rocket fuzes 
see also T-4 fuze 
evaluation, 7 
T-5; 5, 7 
T-6; 5 

time fuze, 15-16 
M-43 mortar shell, 91-95 
M-56 mortar shell, 91-95 
M-166 bomb fuze, 5, 7 
M-168 bomb fuze, 5 
M-381 (booster housing for T-4 fuze), 
40 

Magnetic field machine, 97 
design considerations, 96-97 
function, 96 

ship’s magnetic field intensity, 96 
Mark I photoelectric fuze, 38 
Mark-171 rocket fuze, 5 
Mark-172 rocket fuze, 5 
MC-380 fuzes, 38-40, 76-77 
Mines, ship protection against, 97 
Mortar shells 
M-43; 91-93, 93-95 
M-56; 91-95 
T-25; 91-96 

National Bureau of Standards, 90 
National Carbon Company, 50 
Naval Ordnance Laboratory, 96 

1P24 photocell, 56-57, 85 
Optical fuzes, 18 

PE fuze 

see Photoelectric fuzes 
Philco Corporation, 38, 79 
Photocells, 55-58 
cartridge type, 55 
cesium-antimony surface, 56 
construction, 56-57 


CONFIDENTIAL 


115 



116 


INDEX 


gas-filled, 57 
GL-516; 56 
GL-564 ; 56-57 
IP 24; 56-57, 85 
properties, 57 

sensitivity and spectral response, 56- 
57 

special thyratrons, 57-58 
Photocells, tests, 64-67 
dark current measurement, 67 
gas multiplication measurement, 66- 
67 

sensitivity distribution, 66-67 
visual inspection and mechanical 
tests, 67-68 

Photoelectric fuzes, 20-88 
models developed, 21-23 
objectives, 20 
photocells, 55-58 
principles of operation, 20-21 
use against airborne targets, 24 
Photoelectric fuzes, design, 24-35 
field of view, 25-26 
light level variation, 30-32 
logarithmic response in photocell 
circuit, 30-32 

look-forward angle, 24-25 
mechanical design, 32 
optical design, 33 
power supply, 35 
prevention of sun-firing, 52-55 
radius of action, 26-28 
sensitivity requirements, 24 
Photoelectric fuzes, electrical design, 
33-35 

amplifier, 34, 36-37 
firing circuit, 34 
input circuit, 33-34 
self-destruction circuit, 21, 34 
Photoelectric fuzes, field test methods, 
70-74 

bomb fuzes, 70-71 

radio reporter tests, 70, 73, 86-87 

rocket fuzes, 70-73 

Photoelectric fuzes, laboratory test 
methods 

see T-4 fuze, testing methods 
Photoelectric fuzes, performance tests, 
75-88 

bomb fuzes, 87-88 
experimental rocket fuzes, 86-87 
MC-380 fuzes, 76-77 
revisions of T-4 circuit, 85-86 
service tests on T-4; 75-76 
small target tests with T^ ; 77-84 
sunfiring of T-4 fuzes, 84-85 
T-4 fired from fighter airplane, 76 
Photoelectric fuzes, target analysis, 
28-30 

discrimination of target signals, 29- 
30 


light conditions, 28-29 
threshold sensitivity, 30 
Photoelectric fuzes, types, 36-55 
active-type, 55 

condenser-powered fuzes, 50-52 
generator-powered, 5, 21, 47-50, 88 
Japanese, 18 
model BR (Mark I), 38 
model C, 36-37 

non-sunfiring and non-sunblinding 
fuzes, 52-55 
optical, 18 

T-4; 38-47, 59-69, 77-84 
zero stage fuzes, 55 
Photothyratrons 
condenser-powered fuze, 51 
disadvantages, 57 
Pistol fuze No. 44; 17 
Pressure fuzes, 17 
Proximity fuzes, 16-19 
acoustic, 17-18 
active, 13 
bar-type, 3 

capacitor investigations, 16 
doppler-type, 2 
electrostatic, 17 
energy-sensitive device, 14 
mortar fuze, 91-96 
optical, 18 
passive, 13 
photoelectric, 2-88 
pressure fuzes, 17 
radio, 2-8, 18-19 
T-50 and T-51 ; 3-5 
trench jportar fuzes, 6, 91-92 

R-6236 thyratron, 57 
Radar ranging on shell bursts, 97-98 
Radio link, for cfontrolled-trajectory 
bombs, 98 

Radio Manufacturers Association, 56 
Radio proximity fuzes, 2-8 
active-type, 18 
advantages, 2, 19 
arming process, 3 
bar-type, 3 
bomb fuzes, 5-6 
doppler-type fuze, 2 
evaluation, 6-8 
M-8 rocket fuzes, 5 
operation, 2-3 
passive-type, 2 
principal elements, 2 
requirements for antiaircraft use, 3 
requirements for ground approach, 3 
ring-type, 3 
T-5 ; 5, 7 

Radio reporter for fuze tests, 70, 73, 
86-87 

Ranging on shell bursts, radar, 97-98 
RC time fuzes, 14-17 


advantages, 14 
British UP rocket, 14-15 
capacitor investigations, 16 
M-8 rocket, 15-16 
RCA 936 photocell, 56-57 
RCA C-7071 photothyratron, 57 
Recommendations for future research 
heater cathode thyratrons, 51 
prevention of sunfiring of photoelec- 
tric fuzes, 54 
RPEG fuze, 48 

Revere Copper and Brass Company, 
90 

Ring-type proximity fuze, 3 
ROA (radius of action), photoelectric 
fuzes, 26-28 

Rocket development, 89-91 
Cenco motors, 89-90 
experimental rockets, 89-90 
target rockets for training, 90-91 
Rocket fuzes, 38-52 
condenser-powered fuzes, 50-52, 86 
experimental model tests, 86-87 
field tests, 70-73 
fired from plane, 70-71 
generator-powered, 47-49 
ground-launched, 71-73 
high-angle firing, 71-72 
horizontal firing, 71 
HVAR rocket, 5 
M-8 rocket, 5, 7, 15-16 
Mark I, 38 
Mark 171 and 172; 5 
RC time fuze, 14-16 
RPEB fuze, 82-83 
RPEG fuze, 47-49 
sunproof ed fuzes, 86-87 
T-4; 38-47 
T-5; 5, 7 
T-6 ; 5 
T-30; 5 
T-2004 ; 5-7 
test results, 71-73 
Rocket tossing, 8-10 
RPEB fuzes (rocket, PE, battery), 
tests, 82-83 

RPEG fuzes (rocket, PE, generator), 
47-49 

recommendations for future re- 
search, 48 

turbogenerator assembly, 47 

SCR268 radar for ranging on shell 
bursts, 98 

Self-destruction circuit (SD), photo- 
electric fuze, 34, 38 

Silk substitutes for cartridge bags, 99 
Specifications for photocells, 57 
Sunfiring of photoelectric fuzes, pre* 
vention, 52-55 

double photocell circuits, 52-55 


CONFIDENTIAL 


INDEX 


117 


horizontal firing, 72 
modified input, 54 
recommendations, 54 
sun angle, 52 
sunblinding, 52 
sunproof ed fuzes, 86-87 
T-4 fuze, 84-85 
SW-200 (T-4 fuze switch), 42 
SW-230 (T-4 fuze switch), 40 
Sympathetic functioning of fuzes, 
75-76 

T-4 fuze, 38-47, 59-69, 77-84 
electrical layout, 42 
field of view, 38 
fired from fighter airplane, 76 
general features, 38-41 
ground-approach characteristics, 75 
look-forward angle, 38 
mechanical layout, 40-42 
nose, 38-42 
on bombs, 87 
radius of action, 26 
reliability, 21 
self-destruction circuit, 34 
sunproof modifications, 86-87 
sympathetic functioning, 75-76 
thyrite resistor, 34, 44 
weights and dimensions of compo- 
nents, 40, 43 

T-4 fuze, engineering tolerances, 42-47 
input impedance, 47 
optical system, 43-44 
photocell load resistor, 44-46 
sensitivity, 46 

supply voltage variations, 46 
T-4 fuze, sensitivity tests, 59-62 
dropping ball method, 59 
light level, 62 
mechanical chopping, 59-60 
modulated lamp, 60-62 
pulse test, 59-60 

T-4 fuze, small-target tests, 77^84 


correlation with laboratory tests, 
82-83 

preproduction tests, 80-82 
sensitivity, 81 
series of targets, 82-83 
target hung from poles, 81-84 
T-4 fuze, testing methods, 59-69 
lamp test, 60-62 
lens tests, 67-68 
microphonic test, 86 
nonlinear resistors, 68 
operating tests, 62-63 
pentode tube tests, 68 
photocell tests, 64-67 
service tests, 63-64, 75-76, 80-81 
sunfiring tests, 84-85 
test equipment, 40 
threshold measurements, 62-63 
tube tests, 68 
vibration test, 63 
T-5 fuze, 5, 7 
T-6 rocket fuze, 5 
T-25 mortar shell, 91-96 
design, 93-96 
disadvantages of 
91-93 

stability, 93-95 
T-30 rocket fuze, 5 
T-50 proximity fuze, 3-5 
T-50EI bomb fuze, 5 
T-51 bomb fuze, 5, 7 
T-51 proximity fuze, 3-5 
T-52 bomb fuze, 21, 49, 88 
T-89 bomb fuze, 5 
T-91 bomb fuze, 5-6 
T-92 bomb fuze, 5 
T-132 trench mortar fuze, 6, 91-92 
T-171 trench mortar fuze, 6 
T-172 trench mortar fuze, 6, 91-92 
T-2004 rocket fuze, 5, 7 
Target rockets, 90-91 
launcher, 91 
swaged nozzle, 90 


standard shells, 


swagcu uuzzie, 

LC REGULATION : BEFORE SERVICING 
OR REPRODUCING ANY PART OF THT«5 
DOCUMENT, AL L CL ASSIFICATION 
MARKINGS MUST BE CANCET.T.pn" 


Telemetering for fuze tests, 70, 73, 
86-87 

Television for controlled-trajectory 
bombs, 98 

Threshold sensitivity, photoelectric 
fuzes, 26, 30 

Thyratrons for photocells, 51, 57-58 
Thyrite resistors in photoelectric 
fuzes, 34, 44 
Time fuzes, 14-17 
advantages, 14 
British UP rocket, 14-15 
capacitor investigations, 16 
M-8 rocket, 15-16 
Torpedo tossing, 8-10 
Toss bombing, 8-10 
Trench mortar fuzes, 6, 91-92 
Trench mortar shell (T-25), 91-96 
design, 93-96 

disadvantages of standard shells, 
91-93 

stability, 93-95 

University of Florida, 15 
UP rocket fuze, British, 14-15 
Urea for treating cotton fabrics, 99 

Varistor for T-4 fuze, 34, 44 
VT fuzes 

see Radio proximity fuzes 

Western Electric Company 
magnetic field machine, 96 
MC-380 fuze, 38-40, 76-77 
Westinghouse Electric and Manufac- 
turing Company, 38, 78 
Wurlitzer Corporation, 38, 79 

Yaw reporter for fuze tests, 70, 73, 
86-87 

Zero stage photoelectric fuzes, 55 


_DECLASKTPTi?n 
By authority Secretary 0 f 


Defense m emo 2 A ugust I960 
LIBRARY OF CONGRESS 







THIS ITEM CONTAINS SOME ILLUSTRATIONS WHICH 
CANNOT BE REPRODUCED SATISFACTORILY BY EITHER 
THE ELECTROSTATIC OR THE PHOTOSTATIC PROCESS. 





LC R EGULATION: BEFORE SERVICING 
OR REPRO r '' T, '!iNG AN PART OF THIS 
D0CUM3N ILL CLASSIFICATION 
MA RKINGS MUST BE CANCELLED? 




DECLASSIFIED 
By authority Secretary of 

SEP 1 1960 

Defense memo 2 August 1960 
LIBRARY OF CONGRESS 


• '■£. ~ i * i 


Iff* 


LC ACQUISITIONS 







n fl/IQ >m -ion n 









